While-Loop in C

Syntax of While Loop

The syntax that has been used for the while loop in C programming language is:

while (termination condition) {
  // the body of the loop 
}

Working of While-Loop

1. Initially, we use the parentheses for storing the termination condition of the While loop.
2. Then, there can be two outcomes True or False.
3. Firstly, if the result is true, then the control will automatically execute the body of the loop.
4. It will continue to evaluate again and again until the termination condition is false.
5. Secondly, if the result is false, then the control will definitely come out of the While loop and will dismiss the While Loop.    

Flow chart of While Loop

Here is the diagrammatic presentation, which shows the evaluation of the termination condition (test condition) by while-loop with the help of a flow chart.

Examples of While Loop

Let's understand the entire process with the help of an example:

Example 1: Program of While loop (Increment)

/* Printing integers from 1 to 10 */
#include <stdio.h>
int main () 
{
  int a = 1; // initializing the value of a as 1
  while (a <= 10) // termination condition
  {
    printf ("the value of 'a' is %d\n", a); // body of the while-loop 
    ++a; // increment/ decrement statement
  }
  return 0;
}

Output:

the value of a is 1
the value of a is 2
the value of a is 3
the value of a is 4
the value of a is 5
the value of a is 6
the value of a is 7
the value of a is 8
the value of a is 9
the value of a is 10

Explanation:

Firstly, we initialized the value of the integer variable, which we took as a. Then, we applied a termination condition (while (a <= 10) to avoid the output running to infinity.

After that, we implemented the main body of the while loop just like the following statement:

[Printf ("the value of ‘a’ is %d\n", a);].

This statement prints the desired output that we want (see output). In the main body, we placed an increment statement (++a;). Through this statement, we can get positive integers starting with 1 and ending with 10.

++a statement performs the increment command and will add 1 to the previous value of a.

This evaluation will perform several times until the value of a becomes 11.

When the value of a becomes 11, then it will terminate the entire process because the termination condition gets false as the value of a is greater than 10. So, the loop only executes to the values less than 10 or equal to 10.

Let's see a few more similar examples of while loop.

Example 02: Program of While Loop (decrement):

/* Printing integers from 10 to 1 */
#include <stdio.h>
int main() 
{
  int a = 10; // initializing the value of a as 10
  while (a >= 1) // termination condition
  {
    printf("the value of ‘a’ is %d\n", a); // body of the while-loop 
    --a; // increment/ decrement statement
  }
  return 0;
}

Output:

the value of a is 10
the value of a is 9
the value of a is 8
the value of a is 7
the value of a is 6
the value of a is 5
the value of a is 4
the value of a is 3
the value of a is 2
the value of a is 1

Example 03: Program of while loop with specified starting and ending values:

/* to print the value from a specific point to a specific point */
#include <stdio.h>
int main () 
{
  int a;//initializing 'a' as a value 
  printf ("enter any digit"); //providing a source of input to user  
  scanf ("%d", &a); // assigning the value to a 
  while (a>=1 &&a <=10) //termination condition
  {
    Printf ("\n the value of ‘a’ is %d", a); //body of while-loop
    a++;
  } 
   return 0;
}

Output:

the value of a is 1
 the value of a is 2
 the value of a is 3
 the value of a is 4
 the value of a is 5
 the value of a is 6
 the value of a is 7
 the value of a is 8
 the value of a is 9
 the value of a is 10