C Programming
About TheTutorial
C is a general-purpose, procedural, imperative computer programming language
developed in 1972 by Dennis M. Ritchie at the Bell Telephone Laboratories to
develop the UNIX operating system.
C is the most widely used computer language. It keeps fluctuating at number
one scale of popularity along with Java programming language, which is also
equally popular and most widely used among modern software programmers.
Audience
This tutorial is designed for software programmers with a need to understand
the C programming language starting from scratch. This tutorial will give you
enough understanding on C programming language from where you can take
yourself to higher level of expertise.
Prerequisites
Before proceeding with this tutorial, you should have a basic understanding of
Computer Programming terminologies. A basic understanding of any of the
programming languages will help you in understanding the C programming
concepts and move fast on the learning track.
Copyright & Disclaimer
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Tutorials Point (I) Pvt. Ltd. provides no guarantee regarding the accuracy,
timeliness or completeness of our website or its contents including this tutorial.
If you discover any errors on our website or in this tutorial, please notify us at
contact@tutorialspoint.com
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Table of Contents
About The Tutorial.....................................................................................................................................i
Audience....................................................................................................................................................i
Prerequisites..............................................................................................................................................i
Copyright & Disclaimer ..............................................................................................................................i
Table of Contents......................................................................................................................................ii
1. OVERVIEW .............................................................................................................................. 1
Facts about C ............................................................................................................................................1
Why Use C?...............................................................................................................................................1
C Programs................................................................................................................................................2
2. ENVIORNMENT SETUP ............................................................................................................ 3
Try it Option Online ..................................................................................................................................3
Local Environment Setup ..........................................................................................................................3
Text Editor................................................................................................................................................3
The C Compiler.........................................................................................................................................4
Installation on UNIX/Linux........................................................................................................................4
Installation on Mac OS..............................................................................................................................5
Installation on Windows...........................................................................................................................5
3. PROGRAM STRUCTURE ........................................................................................................... 6
Hello World Example ................................................................................................................................6
Compile and Execute C Program ...............................................................................................................7
4. BASIC SYNTAX ......................................................................................................................... 8
Tokens in C................................................................................................................................................8
Semicolons................................................................................................................................................8
Comments ................................................................................................................................................8
Identifiers .................................................................................................................................................9
iii
Keywords..................................................................................................................................................9
Whitespace in C ......................................................................................................................................10
5. DATA TYPES ........................................................................................................................... 11
Integer Types..........................................................................................................................................11
Floating-Point Types ...............................................................................................................................13
The void Type..........................................................................................................................................14
6. VARIABLES ............................................................................................................................. 15
Variable Definition in C ...........................................................................................................................15
Variable Declaration in C.........................................................................................................................16
Lvalues and Rvalues in C .........................................................................................................................18
7. CONSTANTS AND LITERALS ................................................................................................... 19
Integer Literals........................................................................................................................................19
Floating-point Literals.............................................................................................................................20
Character Constants................................................................................................................................20
String Literals..........................................................................................................................................21
Defining Constants..................................................................................................................................22
The #define Preprocessor ......................................................................................................................22
The const Keyword.................................................................................................................................23
8. STORAGE CLASSES ................................................................................................................. 24
The auto Storage Class............................................................................................................................24
The register Storage Class.......................................................................................................................24
The static Storage Class...........................................................................................................................25
The extern Storage Class.........................................................................................................................26
9. OPERATORS ........................................................................................................................... 28
Arithmetic Operators..............................................................................................................................28
Relational Operators...............................................................................................................................30
iv
Logical Operators....................................................................................................................................32
Bitwise Operators...................................................................................................................................34
Assignment Operators............................................................................................................................37
Misc Operators ↦ sizeof & ternary .........................................................................................................40
Operators Precedence in C......................................................................................................................41
10. DECISION MAKING .............................................................................................................. 45
if Statement............................................................................................................................................46
if…else Statement...................................................................................................................................48
if...else if...else Statement ......................................................................................................................49
Nested if Statements ..............................................................................................................................51
switch Statement....................................................................................................................................53
Nested switch Statements ......................................................................................................................55
The ? : Operator:.....................................................................................................................................57
11. LOOPS ................................................................................................................................. 58
while Loop ..............................................................................................................................................59
for Loop ..................................................................................................................................................61
do…while Loop .......................................................................................................................................63
Nested Loops..........................................................................................................................................65
Loop Control Statements........................................................................................................................67
break Statement.....................................................................................................................................68
continue Statement................................................................................................................................70
goto Statement.......................................................................................................................................72
The Infinite Loop.....................................................................................................................................74
12. FUNCTIONS ......................................................................................................................... 76
Defining a Function.................................................................................................................................76
Function Declarations.............................................................................................................................77
v
Calling a Function....................................................................................................................................78
Function Arguments................................................................................................................................79
Call by Value ...........................................................................................................................................80
Call by Reference ....................................................................................................................................81
13. SCOPE RULES....................................................................................................................... 84
Local Variables........................................................................................................................................84
Global Variables......................................................................................................................................85
Formal Parameters .................................................................................................................................86
Initializing Local and Global Variables.....................................................................................................87
14. ARRAYS ............................................................................................................................... 89
Declaring Arrays......................................................................................................................................89
Initializing Arrays....................................................................................................................................89
Accessing Array Elements .......................................................................................................................90
Arrays in Detail .......................................................................................................................................91
Multidimensional Arrays........................................................................................................................92
Two-dimensional Arrays.........................................................................................................................92
Initializing Two-Dimensional Arrays.......................................................................................................93
Accessing Two-Dimensional Array Elements..........................................................................................93
Passing Arrays to Functions....................................................................................................................94
Return Array from a Function ................................................................................................................96
Pointer to an Array .................................................................................................................................99
15. POINTERS .......................................................................................................................... 101
What are Pointers? ...............................................................................................................................101
How to Use Pointers?............................................................................................................................102
NULL Pointers ......................................................................................................................................103
Pointers in Detail ..................................................................................................................................104
Pointer Arithmetic................................................................................................................................104
Incrementing a Pointer.........................................................................................................................105
vi
Decrementing a Pointer .......................................................................................................................106
Pointer Comparisons............................................................................................................................107
Array of Pointers ..................................................................................................................................108
Pointer to Pointer.................................................................................................................................110
Passing Pointers to Functions ..............................................................................................................112
Return Pointer from Functions ............................................................................................................114
16. STRINGS ............................................................................................................................ 117
17. STRUCTURES ..................................................................................................................... 120
Defining a Structure..............................................................................................................................120
Accessing Structure Members...............................................................................................................121
Structures as Function Arguments ........................................................................................................122
Pointers to Structures...........................................................................................................................124
Bit Fields...............................................................................................................................................126
18. UNIONS ............................................................................................................................. 128
Defining a Union ...................................................................................................................................128
Accessing Union Members....................................................................................................................129
19. BIT FIELDS ......................................................................................................................... 132
Bit Field Declaration..............................................................................................................................133
20. TYPEDEF ............................................................................................................................ 136
typedef vs #define ................................................................................................................................137
21. INPUT AND OUTPUT .......................................................................................................... 139
The Standard Files.................................................................................................................................139
The getchar() and putchar() Functions..................................................................................................139
The gets() and puts() Functions.............................................................................................................140
The scanf() and printf() Functions .........................................................................................................141
22. FILE I/O.............................................................................................................................. 143
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Opening Files ........................................................................................................................................143
Closing a File .........................................................................................................................................144
Writing a File.........................................................................................................................................144
Reading a File........................................................................................................................................145
Binary I/O Functions.............................................................................................................................146
23. PREPROCESSORS ............................................................................................................... 147
Preprocessors Examples........................................................................................................................148
Predefined Macros................................................................................................................................148
Preprocessor Operators........................................................................................................................150
The Macro Continuation (\) Operator..................................................................................................150
The Stringize (#) Operator....................................................................................................................150
The Token Pasting (##) Operator .........................................................................................................150
The Defined() Operator........................................................................................................................151
Parameterized Macros..........................................................................................................................152
24. HEADER FILES .................................................................................................................... 153
Include Syntax.......................................................................................................................................153
Include Operation.................................................................................................................................153
Once-Only Headers...............................................................................................................................154
Computed Includes...............................................................................................................................155
25. TYPE CASTING ................................................................................................................... 156
Integer Promotion ................................................................................................................................157
Usual Arithmetic Conversion.................................................................................................................157
26. ERROR HANDLING ............................................................................................................. 160
errno, perror(), and strerror() ...............................................................................................................160
Divide by Zero Errors.............................................................................................................................161
Program Exit Status...............................................................................................................................162
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27. RECURSION ....................................................................................................................... 164
Number Factorial ..................................................................................................................................164
Fibonacci Series ....................................................................................................................................165
28. VARIABLE ARGUMENTS ..................................................................................................... 167
29. MEMORY MANAGEMENT ................................................................................................. 170
Allocating Memory Dynamically ...........................................................................................................170
Resizing and Releasing Memory............................................................................................................172
30. COMMAND LINE ARGUMENTS .......................................................................................... 174
C Programming
1
C is a general-purpose, high-level language that was originally developed by
Dennis M. Ritchie to develop the UNIX operating system at Bell Labs. C was
originally first implemented on the DEC PDP-11 computer in 1972.
In 1978, Brian Kernighan and Dennis Ritchie produced the first publicly available
description of C, now known as the K&R standard.
The UNIX operating system, the C compiler, and essentially all UNIX application
programs have been written in C. C has now become a widely used professional
language for various reasons:
Easy to learn
Structured language
It produces efficient programs
It can handle low-level activities
It can be compiled on a variety of computer platforms
Facts about C
C was invented to write an operating system called UNIX.
C is a successor of B language which was introduced around the early
1970s.
The language was formalized in 1988 by the American National Standard
Institute (ANSI).
The UNIX OS was totally written in C.
Today C is the most widely used and popular System Programming
Language.
Most of the state-of-the-art software have been implemented using C.
Today's most popular Linux OS and RDBMS MySQL have been written in
C.
Why Use C?
C was initially used for system development work, particularly the programs that
make-up the operating system. C was adopted as a system development
language because it produces code that runs nearly as fast as the code written
in assembly language. Some examples of the use of C might be:
Operating Systems
1. OVERVIEW
C Programming
2
Language Compilers
Assemblers
Text Editors
Print Spoolers
Network Drivers
Modern Programs
Databases
Language Interpreters
Utilities
C Programs
A C program can vary from 3 lines to millions of lines and it should be written
into one or more text files with extension ".c"; for example, hello.c. You can
use "vi", "vim" or any other text editor to write your C program into a file.
This tutorial assumes that you know how to edit a text file and how to write
source code inside a program file.
C Programming
3
Try it Option Online
You really do not need to set up your own environment to start learning C
programming language. Reason is very simple, we already have set up C
Programming environment online, so that you can compile and execute all the
available examples online at the same time when you are doing your theory
work. This gives you confidence in what you are reading and to check the result
with different options. Feel free to modify any example and execute it online.
Try following example using our online compiler option available at
http://www.compileonline.com/.
#include
int main()
{
/* my first program in C */
printf("Hello, World! \n");
return 0;
}
For most of the examples given in this tutorial, you will find the Try it option in
our website code sections at the top right corner that will take you to the online
compiler. So just make use of it and enjoy your learning.
Local Environment Setup
If you want to set up your environment for C programming language, you need
the following two software tools available on your computer, (a) Text Editor and
(b) The C Compiler.
Text Editor
This will be used to type your program. Examples of a few editors include
Windows Notepad, OS Edit command, Brief, Epsilon, EMACS, and vim or vi.
2. ENVIORNMENT SETUP
C Programming
4
The name and version of text editors can vary on different operating systems.
For example, Notepad will be used on Windows, and vim or vi can be used on
Windows as well as on Linux or UNIX.
The files you create with your editor are called the source files and they contain
the program source codes. The source files for C programs are typically named
with the extension ".c".
Before starting your programming, make sure you have one text editor in place
and you have enough experience to write a computer program, save it in a file,
compile it and finally execute it.
The C Compiler
The source code written in source file is the human readable source for your
program. It needs to be "compiled" into machine language so that your CPU can
actually execute the program as per the instructions given.
The compiler compiles the source codes into final executable programs. The
most frequently used and free available compiler is the GNU C/C++ compiler,
otherwise you can have compilers either from HP or Solaris if you have the
respective operating systems.
The following section explains how to install GNU C/C++ compiler on various OS.
m We keep mentioning C/C++ together because GNU gcc compiler works for
both C and C++ programming languages.
Installation on UNIX/Linux
If you are using Linux or UNIX, then check whether GCC is installed on your
system by entering the following command from the command line:
$ gcc -v
If you have GNU compiler installed on your machine, then it should print a
message as follows:
Using built-in specs.
Target: i386-redhat-linux
Configured with: ../configure --prefix=/usr .......
Thread model: posix
gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)
If GCC is not installed, then you will have to install it yourself using the detailed
instructions available at http://gcc.gnu.org/install/.
This tutorial has been written based on Linux and all the given examples have
been compiled on the Cent OS flavor of the Linux system.
C Programming
5
Installation on Mac OS
If you use Mac OS X, the easiest way to obtain GCC is to download the Xcode
development environment from Apple's web site and follow the simple
installation instructions. Once you have Xcode setup, you will be able to use GNU
compiler for C/C++.
Xcode is currently available at developer.apple.com/technologies/tools/.
Installation on Windows
To install GCC on Windows, you need to install MinGW. To install MinGW, go to
the MinGW homepage, www.mingw.org, and follow the link to the MinGW
download page. Download the latest version of the MinGW installation program,
which should be named MinGW-.exe.
While installing MinGW, at a minimum, you must install gcc-core, gcc-g++,
binutils, and the MinGW runtime, but you may wish to install more.
Add the bin subdirectory of your MinGW installation to your PATH environment
variable, so that you can specify these tools on the command line by their simple
names.
After the installation is complete, you will be able to run gcc, g++, ar, ranlib,
dlltool, and several other GNU tools from the Windows command line.
C Programming
6
Before we study the basic building blocks of the C programming language, let us
look at a bare minimum C program structure so that we can take it as a
reference in the upcoming chapters.
Hello World Example
A C program basically consists of the following parts:
Preprocessor Commands
Functions
Variables
Statements & Expressions
Comments
Let us look at a simple code that would print the words "Hello World":
#include
int main()
{
/* my first program in C */
printf("Hello, World! \n");
return 0;
}
Let us take a look at the various parts of the above program:
1. The first line of the program #include is a preprocessor
command, which tells a C compiler to include stdio.h file before going to
actual compilation.
2. The next line int main() is the main function where the program execution
begins.
3. The next line /*...*/ will be ignored by the compiler and it has been put to
add additional comments in the program. So such lines are called
comments in the program.
3. PROGRAM STRUCTURE
C Programming
7
4. The next line printf(...) is another function available in C which causes the
message "Hello, World!" to be displayed on the screen.
5. The next line return 0; terminates the main() function and returns the
value 0.
Compile andExecute C Program
Let us see how to save the source code in a file, and how to compile and run it.
Following are the simple steps:
1. Open a text editor and add the above-mentioned code.
2. Save the file as hello.c
3. Open a command prompt and go to the directory where you have saved
the file.
4. Type gcc hello.c and press enter to compile your code.
5. If there are no errors in your code, the command prompt will take you to
the next line and would generate a.out executable file.
6. Now, type a.out to execute your program.
7. You will see the output "Hello World" printed on the screen.
$ gcc hello.c
$ ./a.out
Hello, World!
Make sure the gcc compiler is in your path and that you are running it in the
directory containing the source file hello.c.
C Programming
8
You have seen the basic structure of a C program, so it will be easy to
understand other basic building blocks of the C programming language.
Tokens in C
A C program consists of various tokens and a token is either a keyword, an
identifier, a constant, a string literal, or a symbol. For example, the following C
statement consists of five tokens:
printf("Hello, World! \n");
The individual tokens are:
printf
(
"Hello, World! \n"
)
;
Semicolons
In a C program, the semicolon is a statement terminator. That is, each individual
statement must be ended with a semicolon. It indicates the end of one logical
entity.
Given below are two different statements:
printf("Hello, World! \n");
return 0;
Comments
Comments are like helping text in your C program and they are ignored by the
compiler. They start with /* and terminate with the characters */ as shown
below:
/* my first program in C */
4. BASIC SYNTAX
C Programming
9
You cannot have comments within comments and they do not occur within a
string or character literals.
Identifiers
A C identifier is a name used to identify a variable, function, or any other userdefined
item. An identifier starts with a letter A to Z, a to z, or an underscore ‘_’
followed by zero or more letters, underscores, and digits (0 to 9).
C does not allow punctuation characters such as @, $, and % within identifiers.
C is a case-sensitive programming language. Thus, Manpower and manpower
are two different identifiers in C. Here are some examples of acceptable
identifiers:
mohd zara abc move_name a_123
myname50 _temp j a23b9 retVal
Keywords
The following list shows the reserved words in C. These reserved words may not
be used as constants or variables or any other identifier names.
auto else long switch
break enum register typedef
case extern return union
char float short unsigned
const for signed void
continue goto sizeof volatile
default if static while
do int struct _Packed
double
C Programming
10
Whitespace in C
A line containing only whitespace, possibly with a comment, is known as a blank
line, and a C compiler totally ignores it.
Whitespace is the term used in C to describe blanks, tabs, newline characters
and comments. Whitespace separates one part of a statement from another and
enables the compiler to identify where one element in a statement, such as int,
ends and the next element begins. Therefore, in the following statement:
int age;
there must be at least one whitespace character (usually a space) between int
and age for the compiler to be able to distinguish them. On the other hand, in
the following statement:
fruit = apples + oranges; // get the total fruit
no whitespace characters are necessary between fruit and =, or between = and
apples, although you are free to include some if you wish to increase readability.
C Programming
11
Data types in C refer to an extensive system used for declaring variables or
functions of different types. The type of a variable determines how much space
it occupies in storage and how the bit pattern stored is interpreted.
The types in C can be classified as follows:
S.N. Types and Description
1 Basic Types:
They are arithmetic types and are further classified into: (a) integer
types and (b) floating-point types.
2 Enumerated types:
They are again arithmetic types and they are used to define variables
that can only assign certain discrete integer values throughout the
program.
3 The type void:
The type specifier void indicates that no value is available.
4 Derived types:
They include (a) Pointer types, (b) Array types, (c) Structure types, (d)
Union types, and (e) Function types.
The array types and structure types are referred collectively as the aggregate
types. The type of a function specifies the type of the function's return value. We
will see the basic types in the following section, whereas other types will be
covered in the upcoming chapters.
Integer Types
The following table provides the details of standard integer types with their
storage sizes and value ranges:
5. DATA TYPES
C Programming
12
Type Storage
size
Value range
char 1 byte -128 to 127 or 0 to 255
unsigned
char
1 byte 0 to 255
signed char 1 byte -128 to 127
int 2 or 4 bytes -32,768 to 32,767 or -2,147,483,648 to
2,147,483,647
unsigned int 2 or 4 bytes 0 to 65,535 or 0 to 4,294,967,295
short 2 bytes -32,768 to 32,767
unsigned
short
2 bytes 0 to 65,535
long 4 bytes -2,147,483,648 to 2,147,483,647
unsigned
long
4 bytes 0 to 4,294,967,295
To get the exact size of a type or a variable on a particular platform, you can
use the sizeof operator. The expressions sizeof(type) yields the storage size of
the object or type in bytes. Given below is an example to get the size of int type
on any machine:
#include
#include
int main()
{
printf("Storage size for int : %d \n", sizeof(int));
C Programming
13
return 0;
}
When you compile and execute the above program, it produces the following
result on Linux:
Storage size for int : 4
Floating-Point Types
The following table provides the details of standard floating-point types with
storage sizes and value ranges and their precision:
Type Storage size Value range Precision
float 4 byte 1.2E-38 to 3.4E+38 6 decimal places
double 8 byte 2.3E-308 to 1.7E+308 15 decimal places
long double 10 byte 3.4E-4932 to 1.1E+4932 19 decimal places
The header file float.h defines macros that allow you to use these values and
other details about the binary representation of real numbers in your programs.
The following example prints the storage space taken by a float type and its
range values:
#include
#include
int main()
{
printf("Storage size for float : %d \n", sizeof(float));
printf("Minimum float positive value: %E\n", FLT_MIN );
printf("Maximum float positive value: %E\n", FLT_MAX );
printf("Precision value: %d\n", FLT_DIG );
return 0;
C Programming
14
}
When you compile and execute the above program, it produces the following
result on Linux:
Storage size for float : 4
Minimum float positive value: 1.175494E-38
Maximum float positive value: 3.402823E+38
Precision value: 6
The void Type
The void type specifies that no value is available. It is used in three kinds of
situations:
S.N. Types and Description
1 Function returns as void
There are various functions in C which do not return any value or you
can say they return void. A function with no return value has the return
type as void. For example, void exit (int status);
2 Function arguments as void
There are various functions in C which do not accept any parameter. A
function with no parameter can accept a void. For example, int
rand(void);
3 Pointers to void
A pointer of type void * represents the address of an object, but not its
type. For example, a memory allocation function void *malloc(size_t
size); returns a pointer to void which can be casted to any data type.
C Programming
15
A variable is nothing but a name given to a storage area that our programs can
manipulate. Each variable in C has a specific type, which determines the size
and layout of the variable's memory; the range of values that can be stored
within that memory; and the set of operations that can be applied to the
variable.
The name of a variable can be composed of letters, digits, and the underscore
character. It must begin with either a letter or an underscore. Upper and
lowercase letters are distinct because C is case-sensitive. Based on the basic
types explained in the previous chapter, there will be the following basic variable
types:
Type Description
char Typically a single octet (one byte). This is an integer type.
int The most natural size of integer for the machine.
float A single-precision floating point value.
double A double-precision floating point value.
void Represents the absence of type.
C programming language also allows to define various other types of variables,
which we will cover in subsequent chapters like Enumeration, Pointer, Array,
Structure, Union, etc. For this chapter, let us study only basic variable types.
Variable Definition in C
A variable definition tells the compiler where and how much storage to create for
the variable. A variable definition specifies a data type and contains a list of one
or more variables of that type as follows:
type variable_list;
6. VARIABLES
C Programming
16
Here, type must be a valid C data type including char, w_char, int, float, double,
bool, or any user-defined object; and variable_list may consist of one or more
identifier names separated by commas. Some valid declarations are shown here:
int i, j, k;
char c, ch;
float f, salary;
double d;
The line int i, j, k; declares and defines the variables i, j and k; which instruct
the compiler to create variables named i, j, and k of type int.
Variables can be initialized (assigned an initial value) in their declaration. The
initializer consists of an equal sign followed by a constant expression as follows:
type variable_name = value;
Some examples are:
extern int d = 3, f = 5; // declaration of d and f.
int d = 3, f = 5; // definition and initializing d and f.
byte z = 22; // definition and initializes z.
char x = 'x'; // the variable x has the value 'x'.
For definition without an initializer: variables with static storage duration are
implicitly initialized with NULL (all bytes have the value 0); the initial value of all
other variables are undefined.
Variable Declaration in C
A variable declaration provides assurance to the compiler that there exists a
variable with the given type and name so that the compiler can proceed for
further compilation without requiring the complete detail about the variable. A
variable declaration has its meaning at the time of compilation only, the
compiler needs actual variable declaration at the time of linking the program.
A variable declaration is useful when you are using multiple files and you define
your variable in one of the files which will be available at the time of linking the
program. You will use the keyword extern to declare a variable at any place.
Though you can declare a variable multiple times in your C program, it can be
defined only once in a file, a function, or a block of code.
Example
Try the following example, where variables have been declared at the top, but
they have been defined and initialized inside the main function:
C Programming
17
#include
// Variable declaration:
extern int a, b;
extern int c;
extern float f;
int main ()
{
/* variable definition: */
int a, b;
int c;
float f;
/* actual initialization */
a = 10;
b = 20;
c = a + b;
printf("value of c : %d \n", c);
f = 70.0/3.0;
printf("value of f : %f \n", f);
return 0;
}
When the above code is compiled and executed, it produces the following result:
value of c : 30
value of f : 23.333334
The same concept applies on function declaration where you provide a function
name at the time of its declaration and its actual definition can be given
anywhere else. For example:
C Programming
18
// function declaration
int func();
int main()
{
// function call
int i = func();
}
// function definition
int func()
{
return 0;
}
Lvalues and Rvalues in C
There are two kinds of expressions in C:
lvalue : Expressions that refer to a memory location are called "lvalue"
expressions. An lvalue may appear as either the left-hand or right-hand
side of an assignment.
rvalue : The term rvalue refers to a data value that is stored at some
address in memory. An rvalue is an expression that cannot have a value
assigned to it which means an rvalue may appear on the right-hand side
but not on the left-hand side of an assignment.
Variables are lvalues and so they may appear on the left-hand side of an
assignment. Numeric literals are rvalues and so they may not be assigned and
cannot appear on the left-hand side. Take a look at the following valid and
invalid statements:
int g = 20; // valid statement
10 = 20; // invalid statement; would generate compile-time error
C Programming
19
Constants refer to fixed values that the program may not alter during its
execution. These fixed values are also called literals.
Constants can be of any of the basic data types like an integer constant, a
floating constant, a character constant, or a string literal. There are enumeration
constants as well.
Constants are treated just like regular variables except that their values cannot
be modified after their definition.
Integer Literals
An integer literal can be a decimal, octal, or hexadecimal constant. A prefix
specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for
decimal.
An integer literal can also have a suffix that is a combination of U and L, for
unsigned and long, respectively. The suffix can be uppercase or lowercase and
can be in any order.
Here are some examples of integer literals:
212 /* Legal */
215u /* Legal */
0xFeeL /* Legal */
078 /* Illegal: 8 is not an octal digit */
032UU /* Illegal: cannot repeat a suffix */
Following are other examples of various types of integer literals:
85 /* decimal */
0213 /* octal */
0x4b /* hexadecimal */
30 /* int */
30u /* unsigned int */
30l /* long */
30ul /* unsigned long */
7. CONSTANTS AND LITERALS
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Floating-point Literals
A floating-point literal has an integer part, a decimal point, a fractional part, and
an exponent part. You can represent floating point literals either in decimal form
or exponential form.
While representing decimal form, you must include the decimal point, the
exponent, or both; and while representing exponential form, you must include
the integer part, the fractional part, or both. The signed exponent is introduced
by e or E.
Here are some examples of floating-point literals:
3.14159 /* Legal */
314159E-5L /* Legal */
510E /* Illegal: incomplete exponent */
210f /* Illegal: no decimal or exponent */
.e55 /* Illegal: missing integer or fraction */
Character Constants
Character literals are enclosed in single quotes, e.g., 'x' can be stored in a
simple variable of char type.
A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g.,
'\t'), or a universal character (e.g., '\u02C0').
There are certain characters in C that represent special meaning when preceded
by a backslash, for example, newline (\n) or tab (\t). Here, you have a list of
such escape sequence codes:
Escape
sequence
Meaning
\\ \ character
\' ' character
\" " character
\? ? character
\a Alert or bell
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21
\b Backspace
\f Form feed
\n Newline
\r Carriage return
\t Horizontal tab
\v Vertical tab
\ooo Octal number of one to three digits
\xhh . . . Hexadecimal number of one or more digits
Following is the example to show a few escape sequence characters:
#include
int main()
{
printf("Hello\tWorld\n\n");
return 0;
}
When the above code is compiled and executed, it produces the following result:
Hello World
String Literals
String literals or constants are enclosed in double quotes "". A string contains
characters that are similar to character literals: plain characters, escape
sequences, and universal characters.
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You can break a long line into multiple lines using string literals and separating
them using whitespaces.
Here are some examples of string literals. All the three forms are identical
strings.
"hello, dear"
"hello, \
dear"
"hello, " "d" "ear"
Defining Constants
There are two simple ways in C to define constants:
Using #define preprocessor
Using const keyword
The #define Preprocessor
Given below is the form to use #define preprocessor to define a constant:
#define identifier value
The following example explains it in detail:
#include
#define LENGTH 10
#define WIDTH 5
#define NEWLINE '\n'
int main()
{
int area;
area = LENGTH * WIDTH;
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23
printf("value of area : %d", area);
printf("%c", NEWLINE);
return 0;
}
When the above code is compiled and executed, it produces the following result:
value of area : 50
The const Keyword
You can use const prefix to declare constants with a specific type as follows:
const type variable = value;
The following example explains it in detail:
#include
int main()
{
const int LENGTH = 10;
const int WIDTH = 5;
const char NEWLINE = '\n';
int area;
area = LENGTH * WIDTH;
printf("value of area : %d", area);
printf("%c", NEWLINE);
return 0;
}
When the above code is compiled and executed, it produces the following result:
value of area : 50
Note that it is a good programming practice to define constants in CAPITALS.
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A storage class defines the scope (visibility) and life-time of variables and/or
functions within a C Program. They precede the type that they modify. We have
four different storage classes in a C program:
auto
register
static
extern
The auto Storage Class
The auto storage class is the default storage class for all local variables.
{
int mount;
auto int month;
}
The example above defines two variables within the same storage class. ‘auto’
can only be used within functions, i.e., local variables.
The register Storage Class
The register storage class is used to define local variables that should be stored
in a register instead of RAM. This means that the variable has a maximum size
equal to the register size (usually one word) and can't have the unary '&'
operator applied to it (as it does not have a memory location).
{
register int miles;
}
The register should only be used for variables that require quick access such as
counters. It should also be noted that defining 'register' does not mean that the
variable will be stored in a register. It means that it MIGHT be stored in a
register depending on hardware and implementation restrictions.
8. STORAGE CLASSES
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25
The static Storage Class
The static storage class instructs the compiler to keep a local variable in
existence during the life-time of the program instead of creating and destroying
it each time it comes into and goes out of scope. Therefore, making local
variables static allows them to maintain their values between function calls.
The static modifier may also be applied to global variables. When this is done, it
causes that variable's scope to be restricted to the file in which it is declared.
In C programming, when static is used on a class data member, it causes only
one copy of that member to be shared by all the objects of its class.
#include
/* function declaration */
void func(void);
static int count = 5; /* global variable */
main()
{
while(count--)
{
func();
}
return 0;
}
/* function definition */
void func( void )
{
static int i = 5; /* local static variable */
i++;
printf("i is %d and count is %d\n", i, count);
}
When the above code is compiled and executed, it produces the following result:
i is 6 and count is 4
i is 7 and count is 3
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i is 8 and count is 2
i is 9 and count is 1
i is 10 and count is 0
The extern Storage Class
The extern storage class is used to give a reference of a global variable that is
visible to ALL the program files. When you use 'extern', the variable cannot be
initialized, however, it points the variable name at a storage location that has
been previously defined.
When you have multiple files and you define a global variable or function, which
will also be used in other files, then extern will be used in another file to provide
the reference of defined variable or function. Just for understanding, extern is
used to declare a global variable or function in another file.
The extern modifier is most commonly used when there are two or more files
sharing the same global variables or functions as explained below.
First File: main.c
#include
int count;
extern void write_extern();
main()
{
count = 5;
write_extern();
}
Second File: support.c
#include
extern int count;
void write_extern(void)
{
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27
printf("count is %d\n", count);
}
Here, extern is being used to declare count in the second file, whereas it has its
definition in the first file, main.c. Now, compile these two files as follows:
$gcc main.c support.c
It will produce the executable program a.out. When this program is executed, it
produces the following result:
5
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28
An operator is a symbol that tells the compiler to perform specific mathematical
or logical functions. C language is rich in built-in operators and provides the
following types of operators:
Arithmetic Operators
Relational Operators
Logical Operators
Bitwise Operators
Assignment Operators
Misc Operators
We will, in this chapter, look into the way each operator works.
Arithmetic Operators
The following table shows all the arithmetic operators supported by the C
language. Assume variable A holds 10 and variable B holds 20, then:
Operator Description Example
+ Adds two operands. A + B = 30
- Subtracts second operand from the first. A - B = -10
* Multiplies both operands. A * B = 200
/ Divides numerator by de-numerator. B / A = 2
% Modulus Operator and remainder of after an
integer division.
B % A = 0
++ Increment operator increases the integer value
by one.
A++ = 11
9. OPERATORS
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29
-- Decrement operator decreases the integer
value by one.
A-- = 9
Example
Try the following example to understand all the arithmetic operators available in
C:
#include
main()
{
int a = 21;
int b = 10;
int c ;
c = a + b;
printf("Line 1 - Value of c is %d\n", c );
c = a - b;
printf("Line 2 - Value of c is %d\n", c );
c = a * b;
printf("Line 3 - Value of c is %d\n", c );
c = a / b;
printf("Line 4 - Value of c is %d\n", c );
c = a % b;
printf("Line 5 - Value of c is %d\n", c );
c = a++;
printf("Line 6 - Value of c is %d\n", c );
c = a--;
printf("Line 7 - Value of c is %d\n", c );
}
When you compile and execute the above program, it produces the following
result:
Line 1 - Value of c is 31
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Line 2 - Value of c is 11
Line 3 - Value of c is 210
Line 4 - Value of c is 2
Line 5 - Value of c is 1
Line 6 - Value of c is 21
Line 7 - Value of c is 22
Relational Operators
The following table shows all the relational operators supported by C. Assume
variable A holds 10 and variable B holds 20, then:
Operator Description Example
== Checks if the values of two operands are equal
or not. If yes, then the condition becomes
true.
(A == B) is not
true.
!= Checks if the values of two operands are equal
or not. If the values are not equal, then the
condition becomes true.
(A != B) is true.
> Checks if the value of left operand is greater
than the value of right operand. If yes, then
the condition becomes true.
(A > B) is not
true.
< Checks if the value of left operand is less than
the value of right operand. If yes, then the
condition becomes true.
(A < B) is true.
>= Checks if the value of left operand is greater
than or equal to the value of right operand. If
yes, then the condition becomes true.
(A >= B) is not
true.
<= Checks if the value of left operand is less than
or equal to the value of right operand. If yes,
then the condition becomes true.
(A <= B) is true.
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31
Example
Try the following example to understand all the relational operators available in
C:
#include
main()
{
int a = 21;
int b = 10;
int c ;
if( a == b )
{
printf("Line 1 - a is equal to b\n" );
}
else
{
printf("Line 1 - a is not equal to b\n" );
}
if ( a < b )
{
printf("Line 2 - a is less than b\n" );
}
else
{
printf("Line 2 - a is not less than b\n" );
}
if ( a > b )
{
printf("Line 3 - a is greater than b\n" );
}
else
{
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printf("Line 3 - a is not greater than b\n" );
}
/* Lets change value of a and b */
a = 5;
b = 20;
if ( a <= b )
{
printf("Line 4 - a is either less than or equal to b\n" );
}
if ( b >= a )
{
printf("Line 5 - b is either greater than or equal to b\n" );
}
}
When you compile and execute the above program, it produces the following
result:
Line 1 - a is not equal to b
Line 2 - a is not less than b
Line 3 - a is greater than b
Line 4 - a is either less than or equal to b
Line 5 - b is either greater than or equal to b
Logical Operators
Following table shows all the logical operators supported by C language. Assume
variable A holds 1 and variable B holds 0, then:
Operator Description Example
&& Called Logical AND operator. If both the
operands are non-zero, then the condition
becomes true.
(A && B) is
false.
|| Called Logical OR Operator. If any of the two
operands is non-zero, then the condition
(A || B) is true.
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33
becomes true.
! Called Logical NOT Operator. It is used to
reverse the logical state of its operand. If a
condition is true, then Logical NOT operator will
make it false.
!(A && B) is
true.
Example
Try the following example to understand all the logical operators available in C:
#include
main()
{
int a = 5;
int b = 20;
int c ;
if ( a && b )
{
printf("Line 1 - Condition is true\n" );
}
if ( a || b )
{
printf("Line 2 - Condition is true\n" );
}
/* lets change the value of a and b */
a = 0;
b = 10;
if ( a && b )
{
printf("Line 3 - Condition is true\n" );
}
else
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34
{
printf("Line 3 - Condition is not true\n" );
}
if ( !(a && b) )
{
printf("Line 4 - Condition is true\n" );
}
}
When you compile and execute the above program, it produces the following
result:
Line 1 - Condition is true
Line 2 - Condition is true
Line 3 - Condition is not true
Line 4 - Condition is true
Bitwise Operators
Bitwise operators work on bits and perform bit-by-bit operation. The truth table
for &, |, and ^ is as follows:
p q p & q p | q p ^ q
0 0 0 0 0
0 1 0 1 1
1 1 1 1 0
1 0 0 1 1
Assume A = 60 and B = 13; in binary format, they will be as follows:
A = 0011 1100
B = 0000 1101
-----------------
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A&B = 0000 1100
A|B = 0011 1101
A^B = 0011 0001
~A = 1100 0011
The following table lists the bitwise operators supported by C. Assume variable
‘A’ holds 60 and variable ‘B’ holds 13, then:
Operator Description Example
& Binary AND Operator copies a bit to the result
if it exists in both operands.
(A & B) = 12, i.e.,
0000 1100
| Binary OR Operator copies a bit if it exists in
either operand.
(A | B) = 61, i.e.,
0011 1101
^ Binary XOR Operator copies the bit if it is set
in one operand but not both.
(A ^ B) = 49, i.e.,
0011 0001
~ Binary Ones Complement Operator is unary
and has the effect of 'flipping' bits.
(~A ) = -61, i.e.,
1100 0011 in 2's
complement form.
<< Binary Left Shift Operator. The left operands
value is moved left by the number of bits
specified by the right operand.
A << 2 = 240,
i.e., 1111 0000
>> Binary Right Shift Operator. The left operands
value is moved right by the number of bits
specified by the right operand.
A >> 2 = 15, i.e.,
0000 1111
Example
Try the following example to understand all the bitwise operators available in C:
#include
main()
{
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36
unsigned int a = 60; /* 60 = 0011 1100 */
unsigned int b = 13; /* 13 = 0000 1101 */
int c = 0;
c = a & b; /* 12 = 0000 1100 */
printf("Line 1 - Value of c is %d\n", c );
c = a | b; /* 61 = 0011 1101 */
printf("Line 2 - Value of c is %d\n", c );
c = a ^ b; /* 49 = 0011 0001 */
printf("Line 3 - Value of c is %d\n", c );
c = ~a; /*-61 = 1100 0011 */
printf("Line 4 - Value of c is %d\n", c );
c = a << 2; /* 240 = 1111 0000 */
printf("Line 5 - Value of c is %d\n", c );
c = a >> 2; /* 15 = 0000 1111 */
printf("Line 6 - Value of c is %d\n", c );
}
When you compile and execute the above program, it produces the following
result:
Line 1 - Value of c is 12
Line 2 - Value of c is 61
Line 3 - Value of c is 49
Line 4 - Value of c is -61
Line 5 - Value of c is 240
Line 6 - Value of c is 15
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Assignment Operators
The following tables lists the assignment operators supported by the C language:
Operator Description Example
= Simple assignment operator. Assigns
values from right side operands to left
side operand.
C = A + B will assign
the value of A + B to
C
+= Add AND assignment operator. It adds the
right operand to the left operand and
assigns the result to the left operand.
C += A is equivalent
to C = C + A
-= Subtract AND assignment operator. It
subtracts the right operand from the left
operand and assigns the result to the left
operand.
C -= A is equivalent
to C = C - A
*= Multiply AND assignment operator. It
multiplies the right operand with the left
operand and assigns the result to the left
operand.
C *= A is equivalent
to C = C * A
/= Divide AND assignment operator. It
divides the left operand with the right
operand and assigns the result to the left
operand.
C /= A is equivalent
to C = C / A
%= Modulus AND assignment operator. It
takes modulus using two operands and
assigns the result to the left operand.
C %= A is equivalent
to C = C % A
<<= Left shift AND assignment operator. C <<= 2 is same as C
= C << 2
>>= Right shift AND assignment operator. C >>= 2 is same as C
= C >> 2
&= Bitwise AND assignment operator. C &= 2 is same as C
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= C & 2
^= Bitwise exclusive OR and assignment
operator.
C ^= 2 is same as C
= C ^ 2
|= Bitwise inclusive OR and assignment
operator.
C |= 2 is same as C =
C | 2
Example
Try the following example to understand all the assignment operators available
in C:
#include
main()
{
int a = 21;
int c ;
c = a;
printf("Line 1 - = Operator Example, Value of c = %d\n", c );
c += a;
printf("Line 2 - += Operator Example, Value of c = %d\n", c );
c -= a;
printf("Line 3 - -= Operator Example, Value of c = %d\n", c );
c *= a;
printf("Line 4 - *= Operator Example, Value of c = %d\n", c );
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c /= a;
printf("Line 5 - /= Operator Example, Value of c = %d\n", c );
c = 200;
c %= a;
printf("Line 6 - %= Operator Example, Value of c = %d\n", c );
c <<= 2;
printf("Line 7 - <<= Operator Example, Value of c = %d\n", c );
c >>= 2;
printf("Line 8 - >>= Operator Example, Value of c = %d\n", c );
c &= 2;
printf("Line 9 - &= Operator Example, Value of c = %d\n", c );
c ^= 2;
printf("Line 10 - ^= Operator Example, Value of c = %d\n", c );
c |= 2;
printf("Line 11 - |= Operator Example, Value of c = %d\n", c );
}
When you compile and execute the above program, it produces the following
result:
Line 1 - = Operator Example, Value of c = 21
Line 2 - += Operator Example, Value of c = 42
Line 3 - -= Operator Example, Value of c = 21
Line 4 - *= Operator Example, Value of c = 441
Line 5 - /= Operator Example, Value of c = 21
Line 6 - %= Operator Example, Value of c = 11
Line 7 - <<= Operator Example, Value of c = 44
Line 8 - >>= Operator Example, Value of c = 11
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Line 9 - &= Operator Example, Value of c = 2
Line 10 - ^= Operator Example, Value of c = 0
Line 11 - |= Operator Example, Value of c = 2
Misc Operators ↦sizeof & ternary
Besides the operators discussed above, there are a few other important
operators including sizeof and ? : supported by the C Language.
Operator Description Example
sizeof() Returns the size of a variable. sizeof(a), where a is
integer, will return 4.
& Returns the address of a variable. &a; returns the actual
address of the
variable.
* Pointer to a variable. *a;
? : Conditional Expression. If Condition is true ?
then value X :
otherwise value Y
Example
Try following example to understand all the miscellaneous operators available in
C:
#include
main()
{
int a = 4;
short b;
double c;
int* ptr;
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/* example of sizeof operator */
printf("Line 1 - Size of variable a = %d\n", sizeof(a) );
printf("Line 2 - Size of variable b = %d\n", sizeof(b) );
printf("Line 3 - Size of variable c= %d\n", sizeof(c) );
/* example of & and * operators */
ptr = &a; /* 'ptr' now contains the address of 'a'*/
printf("value of a is %d\n", a);
printf("*ptr is %d.\n", *ptr);
/* example of ternary operator */
a = 10;
b = (a == 1) ? 20: 30;
printf( "Value of b is %d\n", b );
b = (a == 10) ? 20: 30;
printf( "Value of b is %d\n", b );
}
When you compile and execute the above program, it produces the following
result:
value of a is 4
*ptr is 4.
Value of b is 30
Value of b is 20
Operators Precedence in C
Operator precedence determines the grouping of terms in an expression and
decides how an expression is evaluated. Certain operators have higher
precedence than others; for example, the multiplication operator has a higher
precedence than the addition operator.
For example, x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator *
has a higher precedence than +, so it first gets multiplied with 3*2 and then
adds into 7.
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Here, operators with the highest precedence appear at the top of the table,
those with the lowest appear at the bottom. Within an expression, higher
precedence operators will be evaluated first.
Category Operator Associativity
Postfix () [] -> . ++ - - Left to right
Unary + - ! ~ ++ - - (type)* & sizeof Right to left
Multiplicative * / % Left to right
Additive + - Left to right
Shift << >> Left to right
Relational < <= > >= Left to right
Equality == != Left to right
Bitwise AND & Left to right
Bitwise XOR ^ Left to right
Bitwise OR | Left to right
Logical AND && Left to right
Logical OR || Left to right
Conditional ?: Right to left
Assignment = += -= *= /= %=>>= <<= &= ^= |= Right to left
Comma , Left to right
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Example
Try the following example to understand operator precedence in C:
#include
main()
{
int a = 20;
int b = 10;
int c = 15;
int d = 5;
int e;
e = (a + b) * c / d; // ( 30 * 15 ) / 5
printf("Value of (a + b) * c / d is : %d\n", e );
e = ((a + b) * c) / d; // (30 * 15 ) / 5
printf("Value of ((a + b) * c) / d is : %d\n" , e );
e = (a + b) * (c / d); // (30) * (15/5)
printf("Value of (a + b) * (c / d) is : %d\n", e );
e = a + (b * c) / d; // 20 + (150/5)
printf("Value of a + (b * c) / d is : %d\n" , e );
return 0;
}
When you compile and execute the above program, it produces the following
result:
Value of (a + b) * c / d is : 90
Value of ((a + b) * c) / d is : 90
Value of (a + b) * (c / d) is : 90
Value of a + (b * c) / d is : 50
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C Programming
45
Decision-making structures require that the programmer specifies one or more
conditions to be evaluated or tested by the program, along with a statement or
statements to be executed if the condition is determined to be true, and
optionally, other statements to be executed if the condition is determined to be
false.
Shown below is the general form of a typical decision-making structure found in
most of the programming languages:
C programming language assumes any non-zero and non-null values as true,
and if it is either zero or null, then it is assumed as false value.
C programming language provides the following types of decision-making
statements.
Statement Description
if statement An if statement consists of a boolean expression
followed by one or more statements.
if...else statement An if statement can be followed by an
optional else statement, which executes when
10. DECISION MAKING
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46
the Boolean expression is false.
nested if statements You can use one if or else if statement inside
another if or else if statement(s).
switch statement A switch statement allows a variable to be tested
for equality against a list of values.
nested switch statements You can use one switch statement inside another
switch statement(s).
if Statement
An if statement consists of a Boolean expression followed by one or more
statements.
Syntax
The syntax of an ‘if’ statement in C programming language is:
if(boolean_expression)
{
/* statement(s) will execute if the boolean expression is true */
}
If the Boolean expression evaluates to true, then the block of code inside the ‘if’
statement will be executed. If the Boolean expression evaluates to false, then
the first set of code after the end of the ‘if’ statement (after the closing curly
brace) will be executed.
C programming language assumes any non-zero and non-null values
as true and if it is either zero or null, then it is assumed as false value.
Flow Diagram
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47
Example
#include
int main ()
{
/* local variable definition */
int a = 10;
/* check the boolean condition using if statement */
if( a < 20 )
{
/* if condition is true then print the following */
printf("a is less than 20\n" );
}
printf("value of a is : %d\n", a);
return 0;
}
When the above code is compiled and executed, it produces the following result:
a is less than 20;
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value of a is : 10
if…else Statement
An if statement can be followed by an optional else statement, which executes
when the Boolean expression is false.
Syntax
The syntax of an if...else statement in C programming language is:
if(boolean_expression)
{
/* statement(s) will execute if the boolean expression is true */
}
else
{
/* statement(s) will execute if the boolean expression is false */
}
If the Boolean expression evaluates to true, then the if block will be executed,
otherwise, the else block will be executed.
C programming language assumes any non-zero and non-null values as true,
and if it is either zero or null, then it is assumed as false value.
Flow Diagram
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49
Example
#include
int main ()
{
/* local variable definition */
int a = 100;
/* check the boolean condition */
if( a < 20 )
{
/* if condition is true then print the following */
printf("a is less than 20\n" );
}
else
{
/* if condition is false then print the following */
printf("a is not less than 20\n" );
}
printf("value of a is : %d\n", a);
return 0;
}
When the above code is compiled and executed, it produces the following result:
a is not less than 20;
value of a is : 100
if...else if...else Statement
An if statement can be followed by an optional else if...else statement, which is
very useful to test various conditions using single if...else if statement.
When using if…else if…else statements, there are few points to keep in mind:
An if can have zero or one else's and it must come after any else if's.
An if can have zero to many else if's and they must come before the else.
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Once an else if succeeds, none of the remaining else if's or else's will be
tested.
Syntax
The syntax of an if...else if...else statement in C programming language is:
if(boolean_expression 1)
{
/* Executes when the boolean expression 1 is true */
}
else if( boolean_expression 2)
{
/* Executes when the boolean expression 2 is true */
}
else if( boolean_expression 3)
{
/* Executes when the boolean expression 3 is true */
}
else
{
/* executes when the none of the above condition is true */
}
Example
#include
int main ()
{
/* local variable definition */
int a = 100;
/* check the boolean condition */
if( a == 10 )
{
/* if condition is true then print the following */
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printf("Value of a is 10\n" );
}
else if( a == 20 )
{
/* if else if condition is true */
printf("Value of a is 20\n" );
}
else if( a == 30 )
{
/* if else if condition is true */
printf("Value of a is 30\n" );
}
else
{
/* if none of the conditions is true */
printf("None of the values is matching\n" );
}
printf("Exact value of a is: %d\n", a );
return 0;
}
When the above code is compiled and executed, it produces the following result:
None of the values is matching
Exact value of a is: 100
Nested if Statements
It is always legal in C programming to nest if-else statements, which means you
can use one if or else if statement inside another if or else if statement(s).
Syntax
The syntax for a nested if statement is as follows:
if( boolean_expression 1)
{
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/* Executes when the boolean expression 1 is true */
if(boolean_expression 2)
{
/* Executes when the boolean expression 2 is true */
}
}
You can nest else if...else in the similar way as you have nested if statements.
Example
#include
int main ()
{
/* local variable definition */
int a = 100;
int b = 200;
/* check the boolean condition */
if( a == 100 )
{
/* if condition is true then check the following */
if( b == 200 )
{
/* if condition is true then print the following */
printf("Value of a is 100 and b is 200\n" );
}
}
printf("Exact value of a is : %d\n", a );
printf("Exact value of b is : %d\n", b );
return 0;
}
When the above code is compiled and executed, it produces the following result:
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Value of a is 100 and b is 200
Exact value of a is : 100
Exact value of b is : 200
switch Statement
A switch statement allows a variable to be tested for equality against a list of
values. Each value is called a case, and the variable being switched on is
checked for each switch case.
Syntax
The syntax for a switch statement in C programming language is as follows:
switch(expression){
case constant-expression :
statement(s);
break; /* optional */
case constant-expression :
statement(s);
break; /* optional */
/* you can have any number of case statements */
default : /* Optional */
statement(s);
}
The following rules apply to a switch statement:
The expression used in a switch statement must have an integral or
enumerated type, or be of a class type in which the class has a single
conversion function to an integral or enumerated type.
You can have any number of case statements within a switch. Each case is
followed by the value to be compared to and a colon.
The constant-expression for a case must be the same data type as the
variable in the switch, and it must be a constant or a literal.
When the variable being switched on is equal to a case, the statements
following that case will execute until a break statement is reached.
When a break statement is reached, the switch terminates, and the flow
of control jumps to the next line following the switch statement.
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Not every case needs to contain a break. If no break appears, the flow of
control will fall through to subsequent cases until a break is reached.
A switch statement can have an optional default case, which must
appear at the end of the switch. The default case can be used for
performing a task when none of the cases is true. No break is needed in
the default case.
Flow Diagram
Example
#include
int main ()
{
/* local variable definition */
char grade = 'B';
switch(grade)
{
case 'A' :
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printf("Excellent!\n" );
break;
case 'B' :
case 'C' :
printf("Well done\n" );
break;
case 'D' :
printf("You passed\n" );
break;
case 'F' :
printf("Better try again\n" );
break;
default :
printf("Invalid grade\n" );
}
printf("Your grade is %c\n", grade );
return 0;
}
When the above code is compiled and executed, it produces the following result:
Well done
Your grade is B
Nested switch Statements
It is possible to have a switch as a part of the statement sequence of an outer
switch. Even if the case constants of the inner and outer switch contain common
values, no conflicts will arise.
Syntax
The syntax for a nested switch statement is as follows:
switch(ch1) {
case 'A':
printf("This A is part of outer switch" );
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switch(ch2) {
case 'A':
printf("This A is part of inner switch" );
break;
case 'B': /* case code */
}
break;
case 'B': /* case code */
}
Example
#include
int main ()
{
/* local variable definition */
int a = 100;
int b = 200;
switch(a) {
case 100:
printf("This is part of outer switch\n", a );
switch(b) {
case 200:
printf("This is part of inner switch\n", a );
}
}
printf("Exact value of a is : %d\n", a );
printf("Exact value of b is : %d\n", b );
return 0;
}
When the above code is compiled and executed, it produces the following result:
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This is part of outer switch
This is part of inner switch
Exact value of a is : 100
Exact value of b is : 200
The ? : Operator:
We have covered conditional operator ? : in the previous chapter which can be
used to replace if...else statements. It has the following general form:
Exp1 ? Exp2 : Exp3;
Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of
the colon.
The value of a ? expression is determined like this:
1. Exp1 is evaluated. If it is true, then Exp2 is evaluated and becomes the
value of the entire ? expression.
2. If Exp1 is false, then Exp3 is evaluated and its value becomes the value of
the expression.
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You may encounter situations when a block of code needs to be executed
several number of times. In general, statements are executed sequentially: The
first statement in a function is executed first, followed by the second, and so on.
Programming languages provide various control structures that allow for more
complicated execution paths.
A loop statement allows us to execute a statement or group of statements
multiple times. Given below is the general form of a loop statement in most of
the programming languages:
C programming language provides the following types of loops to handle looping
requirements.
Loop Type Description
while loop Repeats a statement or group of statements while a
given condition is true. It tests the condition before
executing the loop body.
for loop Executes a sequence of statements multiple times and
abbreviates the code that manages the loop variable.
11. LOOPS
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do...while loop It is more like a while statement, except that it tests
the condition at the end of the loop body.
nested loops You can use one or more loops inside any other while,
for, or do..while loop.
while Loop
A while loop in C programming repeatedly executes a target statement as long
as a given condition is true.
Syntax
The syntax of a while loop in C programming language is:
while(condition)
{
statement(s);
}
Here, statement(s) may be a single statement or a block of statements.
The condition may be any expression, and true is any nonzero value. The loop
iterates while the condition is true.
When the condition becomes false, the program control passes to the line
immediately following the loop.
Flow Diagram
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Here, the key point to note is that a while loop might not execute at all. When
the condition is tested and the result is false, the loop body will be skipped and
the first statement after the while loop will be executed.
Example
#include
int main ()
{
/* local variable definition */
int a = 10;
/* while loop execution */
while( a < 20 )
{
printf("value of a: %d\n", a);
a++;
}
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return 0;
}
When the above code is compiled and executed, it produces the following result:
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19
for Loop
A for loop is a repetition control structure that allows you to efficiently write a
loop that needs to execute a specific number of times.
Syntax
The syntax of a for loop in C programming language is:
for ( init; condition; increment )
{
statement(s);
}
Here is the flow of control in a ‘for’ loop:
1. The init step is executed first, and only once. This step allows you to
declare and initialize any loop control variables. You are not required to
put a statement here, as long as a semicolon appears.
2. Next, the condition is evaluated. If it is true, the body of the loop is
executed. If it is false, the body of the loop does not execute and the flow
of control jumps to the next statement just after the ‘for’ loop.
3. After the body of the ‘for’ loop executes, the flow of control jumps back up
to the increment statement. This statement allows you to update any
loop control variables. This statement can be left blank, as long as a
semicolon appears after the condition.
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4. The condition is now evaluated again. If it is true, the loop executes and
the process repeats itself (body of loop, then increment step, and then
again condition). After the condition becomes false, the ‘for’ loop
terminates.
Flow Diagram
Example
#include
int main ()
{
/* for loop execution */
for( int a = 10; a < 20; a = a + 1 )
{
printf("value of a: %d\n", a);
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}
return 0;
}
When the above code is compiled and executed, it produces the following result:
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19
do…while Loop
Unlike for and while loops, which test the loop condition at the top of the loop,
the do...while loop in C programming checks its condition at the bottom of the
loop.
A do...while loop is similar to a while loop, except the fact that it is guaranteed
to execute at least one time.
Syntax
The syntax of a do...while loop in C programming language is:
do
{
statement(s);
}while( condition );
Notice that the conditional expression appears at the end of the loop, so the
statement(s) in the loop executes once before the condition is tested.
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If the condition is true, the flow of control jumps back up to do, and the
statement(s) in the loop executes again. This process repeats until the given
condition becomes false.
Flow Diagram
Example
#include
int main ()
{
/* local variable definition */
int a = 10;
/* do loop execution */
do
{
printf("value of a: %d\n", a);
a = a + 1;
}while( a < 20 );
return 0;
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}
When the above code is compiled and executed, it produces the following result:
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
value of a: 16
value of a: 17
value of a: 18
value of a: 19
Nested Loops
C programming allows to use one loop inside another loop. The following section
shows a few examples to illustrate the concept.
Syntax
The syntax for a nested for loop statement in C is as follows:
for ( init; condition; increment )
{
for ( init; condition; increment )
{
statement(s);
}
statement(s);
}
The syntax for a nested while loop statement in C programming language is as
follows:
while(condition)
{
while(condition)
{
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statement(s);
}
statement(s);
}
The syntax for a nested do...while loop statement in C programming language
is as follows:
do
{
statement(s);
do
{
statement(s);
}while( condition );
}while( condition );
A final note on loop nesting is that you can put any type of loop inside any other
type of loop. For example, a ‘for’ loop can be inside a ‘while’ loop or vice versa.
Example
The following program uses a nested for loop to find the prime numbers from 2
to 100:
#include
int main ()
{
/* local variable definition */
int i, j;
for(i=2; i<100; i++) {
for(j=2; j <= (i/j); j++)
if(!(i%j)) break; // if factor found, not prime
if(j > (i/j)) printf("%d is prime\n", i);
}
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return 0;
}
When the above code is compiled and executed, it produces the following result:
2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime
Loop Control Statements
Loop control statements change execution from its normal sequence. When
execution leaves a scope, all automatic objects that were created in that scope
are destroyed.
C supports the following control statements.
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Control Statement Description
break statement Terminates the loop or switch statement and
transfers execution to the statement immediately
following the loop or switch.
continue statement Causes the loop to skip the remainder of its body and
immediately retest its condition prior to reiterating.
goto statement Transfers control to the labeled statement.
break Statement
The break statement in C programming has the following two usages:
When a break statement is encountered inside a loop, the loop is
immediately terminated and the program control resumes at the next
statement following the loop.
It can be used to terminate a case in the switch statement (covered in
the next chapter).
If you are using nested loops, the break statement will stop the execution of the
innermost loop and start executing the next line of code after the block.
Syntax
The syntax for a break statement in C is as follows:
break;
Flow Diagram
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Example
#include
int main ()
{
/* local variable definition */
int a = 10;
/* while loop execution */
while( a < 20 )
{
printf("value of a: %d\n", a);
a++;
if( a > 15)
{
/* terminate the loop using break statement */
break;
}
}
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return 0;
}
When the above code is compiled and executed, it produces the following result:
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 15
continue Statement
The continue statement in C programming works somewhat like the break
statement. Instead of forcing termination, it forces the next iteration of the loop
to take place, skipping any code in between.
For the for loop, continue statement causes the conditional test and increment
portions of the loop to execute. For the while and do...while loops, continue
statement causes the program control to pass to the conditional tests.
Syntax
The syntax for a continue statement in C is as follows:
continue;
Flow Diagram
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Example
#include
int main ()
{
/* local variable definition */
int a = 10;
/* do loop execution */
do
{
if( a == 15)
{
/* skip the iteration */
a = a + 1;
continue;
}
printf("value of a: %d\n", a);
a++;
}while( a < 20 );
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return 0;
}
When the above code is compiled and executed, it produces the following result:
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 16
value of a: 17
value of a: 18
value of a: 19
goto Statement
A goto statement in C programming provides an unconditional jump from the
‘goto’ to a labeled statement in the same function.
NOTE: Use of goto statement is highly discouraged in any programming
language because it makes difficult to trace the control flow of a program,
making the program hard to understand and hard to modify. Any program that
uses a goto can be rewritten to avoid them.
Syntax
The syntax for a goto statement in C is as follows:
goto label;
..
.
label: statement;
Here label can be any plain text except C keyword and it can be set anywhere in
the C program above or below to goto statement.
Flow Diagram
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Example
#include
int main ()
{
/* local variable definition */
int a = 10;
/* do loop execution */
LOOP:do
{
if( a == 15)
{
/* skip the iteration */
a = a + 1;
goto LOOP;
}
printf("value of a: %d\n", a);
a++;
}while( a < 20 );
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return 0;
}
When the above code is compiled and executed, it produces the following result:
value of a: 10
value of a: 11
value of a: 12
value of a: 13
value of a: 14
value of a: 16
value of a: 17
value of a: 18
value of a: 19
The Infinite Loop
A loop becomes an infinite loop if a condition never becomes false. The for loop
is traditionally used for this purpose. Since none of the three expressions that
form the ‘for’ loop are required, you can make an endless loop by leaving the
conditional expression empty.
#include
int main ()
{
for( ; ; )
{
printf("This loop will run forever.\n");
}
return 0;
}
When the conditional expression is absent, it is assumed to be true. You may
have an initialization and increment expression, but C programmers more
commonly use the for(;;) construct to signify an infinite loop.
NOTE: You can terminate an infinite loop by pressing Ctrl + C keys.
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76
A function is a group of statements that together perform a task. Every C
program has at least one function, which is main(), and all the most trivial
programs can define additional functions.
You can divide up your code into separate functions. How you divide up your
code among different functions is up to you, but logically the division is such
that each function performs a specific task.
A function declaration tells the compiler about a function's name, return type,
and parameters. A function definition provides the actual body of the function.
The C standard library provides numerous built-in functions that your program
can call. For example, strcat() to concatenate two strings, memcpy() to copy
one memory location to another location, and many more functions.
A function can also be referred as a method or a sub-routine or a procedure, etc.
Defining a Function
The general form of a function definition in C programming language is as
follows:
return_type function_name( parameter list )
{
body of the function
}
A function definition in C programming consists of a function header and a
function body. Here are all the parts of a function:
Return Type: A function may return a value. The return_type is the
data type of the value the function returns. Some functions perform the
desired operations without returning a value. In this case, the return_type
is the keyword void.
Function Name: This is the actual name of the function. The function
name and the parameter list together constitute the function signature.
Parameters: A parameter is like a placeholder. When a function is
invoked, you pass a value to the parameter. This value is referred to as
actual parameter or argument. The parameter list refers to the type,
order, and number of the parameters of a function. Parameters are
optional; that is, a function may contain no parameters.
12. FUNCTIONS
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Function Body: The function body contains a collection of statements
that define what the function does.
Example
Given below is the source code for a function called max(). This function takes
two parameters num1 and num2 and returns the maximum value between the
two:
/* function returning the max between two numbers */
int max(int num1, int num2)
{
/* local variable declaration */
int result;
if (num1 > num2)
result = num1;
else
result = num2;
return result;
}
Function Declarations
A function declaration tells the compiler about a function name and how to call
the function. The actual body of the function can be defined separately.
A function declaration has the following parts:
return_type function_name( parameter list );
For the above defined function max(),the function declaration is as follows:
int max(int num1, int num2);
Parameter names are not important in function declaration, only their type is
required, so the following is also a valid declaration:
int max(int, int);
Function declaration is required when you define a function in one source file
and you call that function in another file. In such case, you should declare the
function at the top of the file calling the function.
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Calling a Function
While creating a C function, you give a definition of what the function has to do.
To use a function, you will have to call that function to perform the defined task.
When a program calls a function, the program control is transferred to the called
function. A called function performs a defined task and when its return
statement is executed or when its function-ending closing brace is reached, it
returns the program control back to the main program.
To call a function, you simply need to pass the required parameters along with
the function name, and if the function returns a value, then you can store the
returned value. For example:
#include
/* function declaration */
int max(int num1, int num2);
int main ()
{
/* local variable definition */
int a = 100;
int b = 200;
int ret;
/* calling a function to get max value */
ret = max(a, b);
printf( "Max value is : %d\n", ret );
return 0;
}
/* function returning the max between two numbers */
int max(int num1, int num2)
{
/* local variable declaration */
int result;
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if (num1 > num2)
result = num1;
else
result = num2;
return result;
}
We have kept max()along with main() and compiled the source code. While
running the final executable, it would produce the following result:
Max value is : 200
Function Arguments
If a function is to use arguments, it must declare variables that accept the
values of the arguments. These variables are called the formal parameters of
the function.
Formal parameters behave like other local variables inside the function and are
created upon entry into the function and destroyed upon exit.
While calling a function, there are two ways in which arguments can be passed
to a function:
Call Type Description
Call by value This method copies the actual value of an argument
into the formal parameter of the function. In this case,
changes made to the parameter inside the function
have no effect on the argument.
Call by reference This method copies the address of an argument into
the formal parameter. Inside the function, the address
is used to access the actual argument used in the call.
This means that changes made to the parameter affect
the argument.
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Call by Value
The call by value method of passing arguments to a function copies the actual
value of an argument into the formal parameter of the function. In this case,
changes made to the parameter inside the function have no effect on the
argument.
By default, C programming uses call by value to pass arguments. In general, it
means the code within a function cannot alter the arguments used to call the
function. Consider the function swap() definition as follows.
/* function definition to swap the values */
void swap(int x, int y)
{
int temp;
temp = x; /* save the value of x */
x = y; /* put y into x */
y = temp; /* put temp into y */
return;
}
Now, let us call the function swap() by passing actual values as in the following
example:
#include
/* function declaration */
void swap(int x, int y);
int main ()
{
/* local variable definition */
int a = 100;
int b = 200;
printf("Before swap, value of a : %d\n", a );
printf("Before swap, value of b : %d\n", b );
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/* calling a function to swap the values */
swap(a, b);
printf("After swap, value of a : %d\n", a );
printf("After swap, value of b : %d\n", b );
return 0;
}
Let us put the above code in a single C file, compile and execute it, it will
produce the following result:
Before swap, value of a :100
Before swap, value of b :200
After swap, value of a :100
After swap, value of b :200
It shows that there are no changes in the values, though they had been changed
inside the function.
Call by Reference
The call by reference method of passing arguments to a function copies the
address of an argument into the formal parameter. Inside the function, the
address is used to access the actual argument used in the call. It means the
changes made to the parameter affect the passed argument.
To pass a value by reference, argument pointers are passed to the functions just
like any other value. So accordingly, you need to declare the function
parameters as pointer types as in the following function swap(), which
exchanges the values of the two integer variables pointed to, by their
arguments.
/* function definition to swap the values */
void swap(int *x, int *y)
{
int temp;
temp = *x; /* save the value at address x */
*x = *y; /* put y into x */
*y = temp; /* put temp into y */
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return;
}
Let us now call the function swap() by passing values by reference as in the
following example:
#include
/* function declaration */
void swap(int *x, int *y);
int main ()
{
/* local variable definition */
int a = 100;
int b = 200;
printf("Before swap, value of a : %d\n", a );
printf("Before swap, value of b : %d\n", b );
/* calling a function to swap the values.
* &a indicates pointer to a i.e. address of variable a and
* &b indicates pointer to b i.e. address of variable b.
*/
swap(&a, &b);
printf("After swap, value of a : %d\n", a );
printf("After swap, value of b : %d\n", b );
return 0;
}
Let us put the above code in a single C file, compile and execute it, to produce
the following result:
Before swap, value of a :100
Before swap, value of b :200
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After swap, value of a :200
After swap, value of b :100
It shows that the change has reflected outside the function as well, unlike call
by value where the changes do not reflect outside the function.
By default, C uses call by value to pass arguments. In general, it means the
code within a function cannot alter the arguments used to call the function.
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A scope in any programming is a region of the program where a defined variable
can have its existence and beyond that variable it cannot be accessed. There are
three places where variables can be declared in C programming language:
Inside a function or a block which is called local variables,
Outside of all functions which is called global variables.
In the definition of function parameters which are called formal
parameters.
Let us understand what are local and global variables, and formal parameters.
Local Variables
Variables that are declared inside a function or block are called local variables.
They can be used only by statements that are inside that function or block of
code. Local variables are not known to functions outside their own. The following
example shows how local variables are used. Here all the variables a, b, and c
are local to main() function.
#include
int main ()
{
/* local variable declaration */
int a, b;
int c;
/* actual initialization */
a = 10;
b = 20;
c = a + b;
printf ("value of a = %d, b = %d and c = %d\n", a, b, c);
return 0;
13. SCOPE RULES
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}
Global Variables
Global variables are defined outside a function, usually on top of the program.
Global variables hold their values throughout the lifetime of your program and
they can be accessed inside any of the functions defined for the program.
A global variable can be accessed by any function. That is, a global variable is
available for use throughout your entire program after its declaration. The
following program shows how global variables are used in a program.
#include
/* global variable declaration */
int g;
int main ()
{
/* local variable declaration */
int a, b;
/* actual initialization */
a = 10;
b = 20;
g = a + b;
printf ("value of a = %d, b = %d and g = %d\n", a, b, g);
return 0;
}
A program can have same name for local and global variables but the value of
local variable inside a function will take preference. Here is an example:
#include
/* global variable declaration */
int g = 20;
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int main ()
{
/* local variable declaration */
int g = 10;
printf ("value of g = %d\n", g);
return 0;
}
When the above code is compiled and executed, it produces the following result:
value of g = 10
Formal Parameters
Formal parameters are treated as local variables with-in a function and they take
precedence over global variables. Following is an example:
#include
/* global variable declaration */
int a = 20;
int main ()
{
/* local variable declaration in main function */
int a = 10;
int b = 20;
int c = 0;
printf ("value of a in main() = %d\n", a);
c = sum( a, b);
printf ("value of c in main() = %d\n", c);
return 0;
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}
/* function to add two integers */
int sum(int a, int b)
{
printf ("value of a in sum() = %d\n", a);
printf ("value of b in sum() = %d\n", b);
return a + b;
}
When the above code is compiled and executed, it produces the following result:
value of a in main() = 10
value of a in sum() = 10
value of b in sum() = 20
value of c in main() = 30
Initializing Local and Global Variables
When a local variable is defined, it is not initialized by the system, you must
initialize it yourself. Global variables are initialized automatically by the system
when you define them, as follows:
Data Type Initial Default Value
int 0
char '\0'
float 0
double 0
pointer NULL
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It is a good programming practice to initialize variables properly, otherwise your
program may produce unexpected results, because uninitialized variables will
take some garbage value already available at their memory location.
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Arrays a kind of data structure that can store a fixed-size sequential collection of
elements of the same type. An array is used to store a collection of data, but it
is often more useful to think of an array as a collection of variables of the same
type.
Instead of declaring individual variables, such as number0, number1, ..., and
number99, you declare one array variable such as numbers and use
numbers[0], numbers[1], and ..., numbers[99] to represent individual variables.
A specific element in an array is accessed by an index.
All arrays consist of contiguous memory locations. The lowest address
corresponds to the first element and the highest address to the last element.
Declaring Arrays
To declare an array in C, a programmer specifies the type of the elements and
the number of elements required by an array as follows:
type arrayName [ arraySize ];
This is called a single-dimensional array. The arraySize must be an integer
constant greater than zero and type can be any valid C data type. For example,
to declare a 10-element array called balance of type double, use this statement:
double balance[10];
Here, balance is a variable array which is sufficient to hold up to 10 double
numbers.
Initializing Arrays
You can initialize an array in C either one by one or using a single statement as
follows:
double balance[5] = {1000.0, 2.0, 3.4, 7.0, 50.0};
14. ARRAYS
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The number of values between braces { } cannot be larger than the number of
elements that we declare for the array between square brackets [ ].
If you omit the size of the array, an array just big enough to hold the
initialization is created. Therefore, if you write:
double balance[] = {1000.0, 2.0, 3.4, 7.0, 50.0};
You will create exactly the same array as you did in the previous example.
Following is an example to assign a single element of the array:
balance[4] = 50.0;
The above statement assigns the 5th element in the array with a value of 50.0.
All arrays have 0 as the index of their first element which is also called the base
index and the last index of an array will be total size of the array minus 1.
Shown below is the pictorial representation of the array we discussed above:
Accessing Array Elements
An element is accessed by indexing the array name. This is done by placing the
index of the element within square brackets after the name of the array. For
example:
double salary = balance[9];
The above statement will take the 10th element from the array and assign the
value to salary variable. The following example shows how to use all the three
above-mentioned concepts viz. declaration, assignment, and accessing arrays:
#include
int main ()
{
int n[ 10 ]; /* n is an array of 10 integers */
int i,j;
/* initialize elements of array n to 0 */
for ( i = 0; i < 10; i++ )
{
n[ i ] = i + 100; /* set element at location i to i + 100 */
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}
/* output each array element's value */
for (j = 0; j < 10; j++ )
{
printf("Element[%d] = %d\n", j, n[j] );
}
return 0;
}
When the above code is compiled and executed, it produces the following result:
Element[0] = 100
Element[1] = 101
Element[2] = 102
Element[3] = 103
Element[4] = 104
Element[5] = 105
Element[6] = 106
Element[7] = 107
Element[8] = 108
Element[9] = 109
Arrays in Detail
Arrays are important to C and should need a lot more attention. The following
important concepts related to array should be clear to a C programmer:
Concept Description
Multidimensional arrays C supports multidimensional arrays. The
simplest form of the multidimensional array is
the two-dimensional array.
Passing arrays to functions You can pass to the function a pointer to an
array by specifying the array's name without an
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index.
Return array from a function C allows a function to return an array.
Pointer to an array You can generate a pointer to the first element
of an array by simply specifying the array
name, without any index.
Multidimensional Arrays
C programming language allows multidimensional arrays. Here is the general
form of a multidimensional array declaration:
type name[size1][size2]...[sizeN];
For example, the following declaration creates a three-dimensional integer
array:
int threedim[5][10][4];
Two-dimensional Arrays
The simplest form of multidimensional array is the two-dimensional array. A
two-dimensional array is, in essence, a list of one-dimensional arrays. To declare
a two-dimensional integer array of size [x][y], you would write something as
follows:
type arrayName [ x ][ y ];
Where type can be any valid C data type and arrayName will be a valid C
identifier. A two-dimensional array can be considered as a table which will have
x number of rows and y number of columns. A two-dimensional array a, which
contains three rows and four columns can be shown as follows:
Thus, every element in the array a is identified by an element name of the
form a[ i ][ j ], where ‘a’ is the name of the array, and ‘i' and ‘j’ are the
subscripts that uniquely identify each element in ‘a’.
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Initializing Two-Dimensional Arrays
Multidimensional arrays may be initialized by specifying bracketed values for
each row. Following is an array with 3 rows and each row has 4 columns.
int a[3][4] = {
{0, 1, 2, 3} , /* initializers for row indexed by 0 */
{4, 5, 6, 7} , /* initializers for row indexed by 1 */
{8, 9, 10, 11} /* initializers for row indexed by 2 */
};
The nested braces, which indicate the intended row, are optional. The following
initialization is equivalent to the previous example:
int a[3][4] = {0,1,2,3,4,5,6,7,8,9,10,11};
Accessing Two-Dimensional Array Elements
An element in a two-dimensional array is accessed by using the subscripts, i.e.,
row index and column index of the array. For example:
int val = a[2][3];
The above statement will take the 4th element from the 3rd row of the array.
You can verify it in the above figure. Let us check the following program where
we have used a nested loop to handle a two-dimensional array:
#include
int main ()
{
/* an array with 5 rows and 2 columns*/
int a[5][2] = { {0,0}, {1,2}, {2,4}, {3,6},{4,8}};
int i, j;
/* output each array element's value */
for ( i = 0; i < 5; i++ )
{
for ( j = 0; j < 2; j++ )
{
printf("a[%d][%d] = %d\n", i,j, a[i][j] );
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}
}
return 0;
}
When the above code is compiled and executed, it produces the following result:
a[0][0]: 0
a[0][1]: 0
a[1][0]: 1
a[1][1]: 2
a[2][0]: 2
a[2][1]: 4
a[3][0]: 3
a[3][1]: 6
a[4][0]: 4
a[4][1]: 8
As explained above, you can have arrays with any number of dimensions,
although it is likely that most of the arrays you create will be of one or two
dimensions.
Passing Arrays to Functions
If you want to pass a single-dimension array as an argument in a function, you
would have to declare a formal parameter in one of following three ways and all
three declaration methods produce similar results because each tells the
compiler that an integer pointer is going to be received. Similarly, you can pass
multi-dimensional arrays as formal parameters.
Way-1
Formal parameters as a pointer:
void myFunction(int *param)
{
.
.
.
}
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Way-2
Formal parameters as a sized array:
void myFunction(int param[10])
{
.
.
.
}
Way-3
Formal parameters as an unsized array:
void myFunction(int param[])
{
.
.
.
}
Example
Now, consider the following function, which takes an array as an argument along
with another argument and based on the passed arguments, it returns the
average of the numbers passed through the array as follows:
double getAverage(int arr[], int size)
{
int i;
double avg;
double sum;
for (i = 0; i < size; ++i)
{
sum += arr[i];
}
avg = sum / size;
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return avg;
}
Now, let us call the above function as follows:
#include
/* function declaration */
double getAverage(int arr[], int size);
int main ()
{
/* an int array with 5 elements */
int balance[5] = {1000, 2, 3, 17, 50};
double avg;
/* pass pointer to the array as an argument */
avg = getAverage( balance, 5 ) ;
/* output the returned value */
printf( "Average value is: %f ", avg );
return 0;
}
When the above code is compiled together and executed, it produces the
following result:
Average value is: 214.400000
As you can see, the length of the array doesn't matter as far as the function is
concerned because C performs no bounds checking for formal parameters.
Return Array from a Function
C programming does not allow to return an entire array as an argument to a
function. However, you can return a pointer to an array by specifying the array's
name without an index.
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If you want to return a single-dimension array from a function, you would have
to declare a function returning a pointer as in the following example:
int * myFunction()
{
.
.
.
}
Second point to remember is that C does not advocate to return the address of a
local variable to outside of the function, so you would have to define the local
variable as static variable.
Now, consider the following function which will generate 10 random numbers
and return them using an array and call this function as follows:
#include
/* function to generate and return random numbers */
int * getRandom( )
{
static int r[10];
int i;
/* set the seed */
srand( (unsigned)time( NULL ) );
for ( i = 0; i < 10; ++i)
{
r[i] = rand();
printf( "r[%d] = %d\n", i, r[i]);
}
return r;
}
/* main function to call above defined function */
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int main ()
{
/* a pointer to an int */
int *p;
int i;
p = getRandom();
for ( i = 0; i < 10; i++ )
{
printf( "*(p + %d) : %d\n", i, *(p + i));
}
return 0;
}
When the above code is compiled together and executed, it produces the
following result:
r[0] = 313959809
r[1] = 1759055877
r[2] = 1113101911
r[3] = 2133832223
r[4] = 2073354073
r[5] = 167288147
r[6] = 1827471542
r[7] = 834791014
r[8] = 1901409888
r[9] = 1990469526
*(p + 0) : 313959809
*(p + 1) : 1759055877
*(p + 2) : 1113101911
*(p + 3) : 2133832223
*(p + 4) : 2073354073
*(p + 5) : 167288147
*(p + 6) : 1827471542
*(p + 7) : 834791014
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*(p + 8) : 1901409888
*(p + 9) : 1990469526
Pointer to an Array
It is most likely that you would not understand this section until you are through
with the chapter ‘Pointers’.
Assuming you have some understanding of pointers in C, let us start: An array
name is a constant pointer to the first element of the array. Therefore, in the
declaration:
double balance[50];
balance is a pointer to &balance[0], which is the address of the first element of
the array balance. Thus, the following program fragment assigns p as the
address of the first element of balance:
double *p;
double balance[10];
p = balance;
It is legal to use array names as constant pointers, and vice versa. Therefore,
*(balance + 4) is a legitimate way of accessing the data at balance[4].
Once you store the address of the first element in ‘p’, you can access the array
elements using *p, *(p+1), *(p+2), and so on. Given below is the example to
show all the concepts discussed above:
#include
int main ()
{
/* an array with 5 elements */
double balance[5] = {1000.0, 2.0, 3.4, 17.0, 50.0};
double *p;
int i;
p = balance;
/* output each array element's value */
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printf( "Array values using pointer\n");
for ( i = 0; i < 5; i++ )
{
printf("*(p + %d) : %f\n", i, *(p + i) );
}
printf( "Array values using balance as address\n");
for ( i = 0; i < 5; i++ )
{
printf("*(balance + %d) : %f\n", i, *(balance + i) );
}
return 0;
}
When the above code is compiled and executed, it produces the following result:
Array values using pointer
*(p + 0) : 1000.000000
*(p + 1) : 2.000000
*(p + 2) : 3.400000
*(p + 3) : 17.000000
*(p + 4) : 50.000000
Array values using balance as address
*(balance + 0) : 1000.000000
*(balance + 1) : 2.000000
*(balance + 2) : 3.400000
*(balance + 3) : 17.000000
*(balance + 4) : 50.000000
In the above example, p is a pointer to double, which means it can store the
address of a variable of double type. Once we have the address in p, *p will give
us the value available at the address stored in p, as we have shown in the above
example.
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Pointers in C are easy and fun to learn. Some C programming tasks are
performed more easily with pointers, and other tasks, such as dynamic memory
allocation, cannot be performed without using pointers. So it becomes necessary
to learn pointers to become a perfect C programmer. Let's start learning them in
simple and easy steps.
As you know, every variable is a memory location and every memory location
has its address defined which can be accessed using ampersand (&) operator,
which denotes an address in memory. Consider the following example, which
prints the address of the variables defined:
#include
int main ()
{
int var1;
char var2[10];
printf("Address of var1 variable: %x\n", &var1 );
printf("Address of var2 variable: %x\n", &var2 );
return 0;
}
When the above code is compiled and executed, it produces the following result:
Address of var1 variable: bff5a400
Address of var2 variable: bff5a3f6
What are Pointers?
A pointer is a variable whose value is the address of another variable, i.e.,
direct address of the memory location. Like any variable or constant, you must
declare a pointer before using it to store any variable address. The general form
of a pointer variable declaration is:
15. POINTERS
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type *var-name;
Here, type is the pointer's base type; it must be a valid C data type and varname
is the name of the pointer variable. The asterisk * used to declare a
pointer is the same asterisk used for multiplication. However, in this statement,
the asterisk is being used to designate a variable as a pointer. Take a look at
some of the valid pointer declarations:
int *ip; /* pointer to an integer */
double *dp; /* pointer to a double */
float *fp; /* pointer to a float */
char *ch /* pointer to a character */
The actual data type of the value of all pointers, whether integer, float,
character, or otherwise, is the same, a long hexadecimal number that represents
a memory address. The only difference between pointers of different data types
is the data type of the variable or constant that the pointer points to.
How to Use Pointers?
There are a few important operations, which we will do with the help of pointers
very frequently. (a) We define a pointer variable, (b) assign the address of a
variable to a pointer, and (c) finally access the value at the address available in
the pointer variable. This is done by using unary operator * that returns the
value of the variable located at the address specified by its operand. The
following example makes use of these operations:
#include
int main ()
{
int var = 20; /* actual variable declaration */
int *ip; /* pointer variable declaration */
ip = &var; /* store address of var in pointer variable*/
printf("Address of var variable: %x\n", &var );
/* address stored in pointer variable */
printf("Address stored in ip variable: %x\n", ip );
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/* access the value using the pointer */
printf("Value of *ip variable: %d\n", *ip );
return 0;
}
When the above code is compiled and executed, it produces the following result:
Address of var variable: bffd8b3c
Address stored in ip variable: bffd8b3c
Value of *ip variable: 20
NULL Pointers
It is always a good practice to assign a NULL value to a pointer variable in case
you do not have an exact address to be assigned. This is done at the time of
variable declaration. A pointer that is assigned NULL is called a null pointer.
The NULL pointer is a constant with a value of zero defined in several standard
libraries. Consider the following program:
#include
int main ()
{
int *ptr = NULL;
printf("The value of ptr is : %x\n", ptr );
return 0;
}
When the above code is compiled and executed, it produces the following result:
The value of ptr is 0
In most of the operating systems, programs are not permitted to access
memory at address 0 because that memory is reserved by the operating system.
However, the memory address 0 has special significance; it signals that the
pointer is not intended to point to an accessible memory location. But by
convention, if a pointer contains the null (zero) value, it is assumed to point to
nothing.
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To check for a null pointer, you can use an ‘if’ statement as follows:
if(ptr) /* succeeds if p is not null */
if(!ptr) /* succeeds if p is null */
Pointers in Detail
Pointers have many but easy concepts and they are very important to C
programming. The following important pointer concepts should be clear to any C
programmer:
Concept Description
Pointer arithmetic There are four arithmetic operators that
can be used in pointers: ++, --, +, -
Array of pointers You can define arrays to hold a number of
pointers.
Pointer to pointer C allows you to have pointer on a pointer
and so on.
Passing pointers to functions in C Passing an argument by reference or by
address enable the passed argument to be
changed in the calling function by the
called function.
Return pointer from functions in C C allows a function to return a pointer to
the local variable, static variable, and
dynamically allocated memory as well.
Pointer Arithmetic
A pointer in C is an address, which is a numeric value. Therefore, you can
perform arithmetic operations on a pointer just as you can on a numeric value.
There are four arithmetic operators that can be used on pointers: ++, --, +, and
-
To understand pointer arithmetic, let us consider that ptr is an integer pointer
which points to the address 1000. Assuming 32-bit integers, let us perform the
following arithmetic operation on the pointer:
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ptr++
After the above operation, the ptr will point to the location 1004 because each
time ptr is incremented, it will point to the next integer location which is 4 bytes
next to the current location. This operation will move the pointer to the next
memory location without impacting the actual value at the memory location.
If ptr points to a character whose address is 1000, then the above operation will
point to the location 1001 because the next character will be available at 1001.
Incrementing a Pointer
We prefer using a pointer in our program instead of an array because the
variable pointer can be incremented, unlike the array name which cannot be
incremented because it is a constant pointer. The following program increments
the variable pointer to access each succeeding element of the array:
#include
const int MAX = 3;
int main ()
{
int var[] = {10, 100, 200};
int i, *ptr;
/* let us have array address in pointer */
ptr = var;
for ( i = 0; i < MAX; i++)
{
printf("Address of var[%d] = %x\n", i, ptr );
printf("Value of var[%d] = %d\n", i, *ptr );
/* move to the next location */
ptr++;
}
return 0;
}
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When the above code is compiled and executed, it produces the following result:
Address of var[0] = bf882b30
Value of var[0] = 10
Address of var[1] = bf882b34
Value of var[1] = 100
Address of var[2] = bf882b38
Value of var[2] = 200
Decrementing a Pointer
The same considerations apply to decrementing a pointer, which decreases its
value by the number of bytes of its data type as shown below:
#include
const int MAX = 3;
int main ()
{
int var[] = {10, 100, 200};
int i, *ptr;
/* let us have array address in pointer */
ptr = &var[MAX-1];
for ( i = MAX; i > 0; i--)
{
printf("Address of var[%d] = %x\n", i, ptr );
printf("Value of var[%d] = %d\n", i, *ptr );
/* move to the previous location */
ptr--;
}
return 0;
}
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When the above code is compiled and executed, it produces the following result:
Address of var[3] = bfedbcd8
Value of var[3] = 200
Address of var[2] = bfedbcd4
Value of var[2] = 100
Address of var[1] = bfedbcd0
Value of var[1] = 10
Pointer Comparisons
Pointers may be compared by using relational operators, such as ==, <, and >.
If p1 and p2 point to variables that are related to each other, such as elements
of the same array, then p1 and p2 can be meaningfully compared.
The following program modifies the previous example - one by incrementing the
variable pointer so long as the address to which it points is either less than or
equal to the address of the last element of the array, which is &var[MAX - 1]:
#include
const int MAX = 3;
int main ()
{
int var[] = {10, 100, 200};
int i, *ptr;
/* let us have address of the first element in pointer */
ptr = var;
i = 0;
while ( ptr <= &var[MAX - 1] )
{
printf("Address of var[%d] = %x\n", i, ptr );
printf("Value of var[%d] = %d\n", i, *ptr );
/* point to the previous location */
ptr++;
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i++;
}
return 0;
}
When the above code is compiled and executed, it produces the following result:
Address of var[0] = bfdbcb20
Value of var[0] = 10
Address of var[1] = bfdbcb24
Value of var[1] = 100
Address of var[2] = bfdbcb28
Value of var[2] = 200
Array of Pointers
Before we understand the concept of arrays of pointers, let us consider the
following example, which uses an array of 3 integers:
#include
const int MAX = 3;
int main ()
{
int var[] = {10, 100, 200};
int i;
for (i = 0; i < MAX; i++)
{
printf("Value of var[%d] = %d\n", i, var[i] );
}
return 0;
}
When the above code is compiled and executed, it produces the following result:
Value of var[0] = 10
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Value of var[1] = 100
Value of var[2] = 200
There may be a situation when we want to maintain an array, which can store
pointers to an int or char or any other data type available. Following is the
declaration of an array of pointers to an integer:
int *ptr[MAX];
It declares ptr as an array of MAX integer pointers. Thus, each element in ptr
holds a pointer to an int value. The following example uses three integers, which
are stored in an array of pointers, as follows:
#include
const int MAX = 3;
int main ()
{
int var[] = {10, 100, 200};
int i, *ptr[MAX];
for ( i = 0; i < MAX; i++)
{
ptr[i] = &var[i]; /* assign the address of integer. */
}
for ( i = 0; i < MAX; i++)
{
printf("Value of var[%d] = %d\n", i, *ptr[i] );
}
return 0;
}
When the above code is compiled and executed, it produces the following result:
Value of var[0] = 10
Value of var[1] = 100
Value of var[2] = 200
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You can also use an array of pointers to character to store a list of strings as
follows:
#include
const int MAX = 4;
int main ()
{
char *names[] = {
"Zara Ali",
"Hina Ali",
"Nuha Ali",
"Sara Ali",
};
int i = 0;
for ( i = 0; i < MAX; i++)
{
printf("Value of names[%d] = %s\n", i, names[i] );
}
return 0;
}
When the above code is compiled and executed, it produces the following result:
Value of names[0] = Zara Ali
Value of names[1] = Hina Ali
Value of names[2] = Nuha Ali
Value of names[3] = Sara Ali
Pointer to Pointer
A pointer to a pointer is a form of multiple indirection, or a chain of pointers.
Normally, a pointer contains the address of a variable. When we define a pointer
to a pointer, the first pointer contains the address of the second pointer, which
points to the location that contains the actual value as shown below.
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A variable that is a pointer to a pointer must be declared as such. This is done
by placing an additional asterisk in front of its name. For example, the following
declaration declares a pointer to a pointer of type int:
int **var;
When a target value is indirectly pointed to by a pointer to a pointer, accessing
that value requires that the asterisk operator be applied twice, as is shown
below in the example:
#include
int main ()
{
int var;
int *ptr;
int **pptr;
var = 3000;
/* take the address of var */
ptr = &var;
/* take the address of ptr using address of operator & */
pptr = &ptr;
/* take the value using pptr */
printf("Value of var = %d\n", var );
printf("Value available at *ptr = %d\n", *ptr );
printf("Value available at **pptr = %d\n", **pptr);
return 0;
}
When the above code is compiled and executed, it produces the following result:
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Value of var = 3000
Value available at *ptr = 3000
Value available at **pptr = 3000
Passing Pointers to Functions
C programming allows passing a pointer to a function. To do so, simply declare
the function parameter as a pointer type.
Following is a simple example where we pass an unsigned long pointer to a
function and change the value inside the function which reflects back in the
calling function:
#include
#include
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