Working of While Loop With Examples

What is a while Loop in C++?

A while Loop in C++ and C Language is used to execute a block of one or more statements repeatedly as long as the given condition remains TRUE.

When To Use a while Loop in C++?

A while Loop is suitable in a condition where the number of iteratios is not known in advance.

Syntax of while Loop in C++

while(condition) 
       statement;

Where:

• while is the reserved word.

• condition is a valid C++ relational expression. For example i>=1   or k<=5

• statement is a C++ instruction. This instruction will be executed repeatedly as long as the given condition remains true.

or

 while(condition)
{
    statement 1;
    statement 2;
   .
   .
   .
     statement N;
 }

Where:

• while is the reserved word.

• condition is a valid C++ relational expression. For example i>=1   or k<=5

• {
      statement 1;
      statement 2;
     .
     .
     .
       statement N;
   }
  Statement BLOCK or a compound statement   A set of one or more statements enclosed in BRACES { } is called a statement block or a Compound Statement. This block will be executed repeatedly as long as the given condition remains true. This statement block is also called body of loop or Loop Body.
  
  

  Working of a while loop

  We will explain the working of a while loop in C++ with the help of an example loop statement as follows:
  
  int counter = 1;
  
  while ( counter <=3 )
  {
         cout<<"while LOOP"<<endl;
         counter ++;
  }
  
  Explanation:
  First of all, a loop control variable called "counter" is initialized to 1.
  

  FIRST ITERATION

  Working of while loop starts by checking the condition ( counter<=3 ). Now the value of counter is 1. So that the condition becomes 1<=3 which produces true result. Therefore, loop body that is
  {
         cout<<"while LOOP"<<endl;
         counter ++;
  }
  will be executed. while LOOP will be printed on screen and cursor will move to next line because of endl. counter variable will be incremented by 1 so that it has the new value 2.
  
  
  

  SECOND ITERATION

  The control will move to start of while loop. Condition is checked ( counter<=3 ). Now the value of counter is 2. So that the condition becomes 2<=3 which produces true result. Therefore, loop body that is
  {
         cout<<"while LOOP"<<endl;
         counter ++;
  }
  will be executed. while LOOP will be printed on screen for second time and cursor will move to next line because of endl. counter variable will be incremented by 1 so that it has the new value 3.
  
  
  

  THIRD ITERATION

  The control will move to start of while loop. Condition is checked ( counter<=3 ). Now the value of counter is 3. So that the condition becomes 3<=3 which produces true result. Therefore, loop body that is
  {
         cout<<"while LOOP"<<endl;
         counter ++;
  }
  will be executed. while LOOP will be printed on screen for third time and cursor will move to next line because of endl. counter variable will be incremented by 1 so that it has the new value 4.
  
  Now the control will move to the start of while loop. The condition ( counter <=3 ) is tested. Since the value of counter variable is 4 now. Hence the condition becomes  4<=3 which will give false now. This will cause the while loop to end.
  
  

  Example Code 2: Display the numbers 5 down to 1 with the help of while loop.

   

  int k=5;
  while( k >=1)
  {
      cout<<k<<endl;
      k--;
  }
   
  
  Explanation:
  First of all, a loop control variable called "k" is initialized to 5.
  

  FIRST ITERATION

  Working of while loop starts by checking the condition ( k>=1 ). Now the value of counter is 5. So that the condition becomes  5>=1 which produces true result. Therefore, loop body that is
  {
      cout<<k<<endl;
      k--;
  }
  will be executed. The value of k that is 5 will be printed on screen and cursor will move to next line because of endl. counter variable k will be decremented by 1 so that it has the new value 4.
  
  
  

  SECOND ITERATION

  The control will move to start of while loop. Condition is checked (  k>=1 ). Now the value of counter is 4. So that the condition becomes  4>=1 which produces true result. Therefore, loop body that is
  {
      cout<<k<<endl;
      k--;
  }
  will be executed. The value of k that is 4 will be printed on screen and cursor will move to next line because of endl. counter variable k will be decremented by 1 so that it has the new value 3.
  
  
  

  THIRD ITERATION

  The control will move to start of while loop. Condition is checked (  k>=1 ). Now the value of counter is 3. So that the condition becomes  3>=1 which produces true result. Therefore, loop body that is
  {
      cout<<k<<endl;
      k--;
  }
  will be executed. The value of k that is 3 will be printed on screen and cursor will move to next line because of endl. counter variable will be decremented by 1 so that it has the new value 2.
  
  

  FOURTH ITERATION

  The control will move to start of while loop. Condition is checked (  k>=1 ). Now the value of counter is 2. So that the condition becomes  2>=1 which produces true result. Therefore, loop body that is
  {
      cout<<k<<endl;
      k--;
  }
  will be executed. The value of k that is 2 will be printed on screen and cursor will move to next line because of endl. counter variable will be decremented by 1 so that it has the new value 1.
  
  
  

  FIFTH ITERATION

  The control will move to start of while loop. Condition is checked (  k>=1 ). Now the value of counter is 3. So that the condition becomes  1>=1 which produces true result. Therefore, loop body that is
  {
      cout<<k<<endl;
      k--;
  }
  will be executed. The value of k that is 1 will be printed on screen and cursor will move to next line because of endl. counter variable will be decremented by 1 so that it has the new value 0.
  
  Now the control will move to the start of while loop. The condition (  k>=1 ) is tested. Since the value of counter variable is 4 now. Hence the condition becomes   0>=1 which will give false now. This will cause the while loop to end.