In
every programming language, thus also in the C programming language, there are
circumstances were you want to do the same thing many times. For instance you
want to print the same words ten times. You could type ten printf function, but
it is easier to use a loop. The only thing you have to do is to setup loops
that execute the same printf function ten times.
There are three basic types of loops which are:
There are three basic types of loops which are:
§
“for loop”
§
“while loop”
§
“do while loop”
A loop allows us to
execute a statement or group of statements multiple times. C programming
language provides the following types of loop to handle looping requirements.
Loop Type
|
Description
|
Execute a sequence of statements multiple times and abbreviates
the code that manages the loop variable.
|
|
Repeats a statement or group of statements while a given
condition is true. It tests the condition before executing the loop body.
|
|
Like a while statement, except that it tests the condition at
the end of the loop body
|
|
You can use one or more loop inside any another while, for or
do..while loop.
|
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 ( initialization ; condition; increment )
{
statement(s);
}
Here is the flow of
control in a for loop:
1. The initialization 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 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.
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 CHART:
Example:
#include
<stdio.h>
#include<conio.h>
void main ()
{
for( int a = 10; a < 20; a = a + 1 )
{
printf("value of a: %d\n", a);
}
getch();
}
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
"While Loop"
A while loop statement in C programming
language repeatedly executes a target statement as long as a given condition is
true.
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, program control passes to
the line immediately following the loop.
Flow Diagram:
#include <stdio.h>
#include<conio.h>
void main ()
{
int a = 10;
while( a < 20 )
{
printf("value
of a: %d\n", a);
a++;
}
getch();
}
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 language checks
its condition at the bottom of the loop.
A do...while loop is similar to a while loop,
except that a do...while loop 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 execute once before the condition
is tested.
If the condition is true, the flow of control jumps back up
to do, and the statement(s) in the loop execute again. This process repeats
until the given condition becomes false.
Flow Diagram:
Example:
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