Looping
It is used to execute group of statement repeatedly till the condition is satisfy.
C support three types of looping statement.1.while loop
2.do while loop
3.for loop.
Basically in looping statement three things are included and that are most important .
1 initialization 2 condition
3 updation .
By using initialization we initialize the variable and after that it check the condition and in updation it increment or decrement the variable.
1.While loop
When we don’t know the ending point of any execution at that time we used while loop .it is used execute the group of statement repeatedly till condition is satisfy.
Syntax: Initialization ;
While(condition)
{
Block of statement//
}
Flowchart 
Ex:WAP to print hello world using while loop
#include<stdio.h>
#include<conio.h>
void main()
{
int i=1;
clrscr();
while(i<=5)
{
printf("\n Hello world");
i++;
}
getch();
}
o/p Hello world
Hello world
Hello world
Hello world
Hello world
Do while loop
The main difference here is the condition is tested after the body of the loop and the statement in the body will be executed at least once whether the condition is true or false. This is not the case with the other two loops where if the condition is false at the beginning, then the body of the loop is not executed at all. Notice the semicolon at the end of the while line of code.
Syntax: initialization;
do
{
Block of statement//
}while(condition);
Flowchart 
EX: Find the factorial of a number
#include<stdio.h>
#include<conio.h>
main()
{
int n, num, factorial = 1;
printf ("Enter the number:");
scanf ("%d", &n);
num = n;
if (n < 0)
printf ("\n factorial of negative number not possible:");
else
if (n = = 0)
printf ("Factorial of 0 is 1 \n");
else
do
{
factorial * = n;
n - -;
}
while (n > 1);
printf ("factorial of % d = % d", no, fact);
}
o/p
if the value entered is 5, the program outputs 120 (i.e., 5 * 4 * 3 * 2 * 1).
3.For Loop
A for loop allows execution of a statement (or a block of statements) repeatedly a number of times. When the number of times a statement is to be executed is known in advance, for loop is particularly useful. The syntax of for loop in C language is as follows
Syntax:
for(<initialization>; <condition>; <modification>)
{
statement-1;
}
Flowchart 
EX: program to print number from 1 to 5
#include<stdio.h>
#include<conio.h>
main( )
{
int i;
clrscr();
for (i = 1; i <= 5; i ++)
printf ("%d \n", i);
getch();
}
o/p1 2 3 4 5