Flow chart of While loop in C

This is a flowchart that represents the process of executing the while loop in the C programming language.
Generally, as we know there are three main components of while loop:
1. The initialization statement,
2. The termination condition, and
3. The update statement which helps in altering the value while further execution.

Here, you can see that the first step is to declare the variable and initialize its value with the help of assignment operator.

In the next step, we will have to use a test expression that will certainly help in dismissing the while loop or from preventing it to run toward infinity as per the requirement. If the termination condition or test expression is true then the control will go to the main body of the loop.
The last component of while loop is the increment or decrement statement that will be executed after the execution of the body.

This execution will terminate here. And, the loop will go to execute while next time and check whether the value returned by the termination condition is true or false. Loop will continue to execute until the condition becomes false. As the value is found to be false then the control will come out of the loop and the loop will completely dismissed.

Example of while Loop: Here is program in c that will print numbers from 11 to 20 with the help of while loop:

#include <stdio.h>
int main() 
{
  int a=11; /* declaring a variable ‘a’ and initializing its value as 11*/
  while (a <= 20)
/* a must be less than 20 */
  {
    printf ("%d ", a);
/* printing final value of variable ‘a’ */
++a;
/* modifying statement */
  return 0;
}	

Explanation:

Initially we declared a variable ‘a’. Then, we have while loop syntax that contains 3 main components which are as follows:

1. a=11                 (Initialization statement)
2. a<=20     (termination condition)
3. ++a                   (increment or decrement statement)

In this, the value of ‘a’ will begin with 11, and the termination condition will check that the value of ‘a’ is smaller than 20 or not. After this, there is modifying statement that helps in altering the value of ‘a’ so that further evaluations can be done. This can be pre-increment, post-increment, pre-decrement, or post-decrement. When the value of ‘a’ goes higher than 20 then the termination condition will terminate the while loop.

Two More Examples of while Loop

Example 1:

#include <stdio.h>
int main() 
{
  int a=11; 
/* declaring a variable ‘a’ and initializing its value as 11*/
  while (a >= 2)
/* a must be more than 2 */
  {
    printf ("%d ", a);
/* printing final value of variable ‘a’ */
--a;
/* modifying statement */
  }
  return 0;
}		

Example 2:               

#include <stdio.h>
int main()
{
    int a=0, b=1, c = 0;
/* declaring a variable ‘a’ ‘b’ ‘c’ and initializing values*/
    printf("Enter a positive integer: ");
    scanf("%d", &a);
    while (b <= a)
/* initializing its value as 1; a must be less than a; modifying statement */
    {
        c += b;
    }
    printf("c = %d", c);
/* printing final value of variable ‘c’ */
--b;
/* modifying statement */
    return 0;
}