While Loops

C++ While Loop Syntax

while (testExpression) 
{
     // codes  
}

where, testExpression is checked on each entry of the while loop.

How while loop works?

• The while loop evaluates the test expression.

• If the test expression is true, codes inside the body of while loop is evaluated.

• Then, the test expression is evaluated again. This process goes on until the test expression is false.

• When the test expression is false, while loop is terminated.

Flowchart of while Loop

Flowchart of while loop in C++ Programming

Example 1: C++ while Loop

// C++ Program to compute factorial of a number
// Factorial of n = 1*2*3...*n

#include <iostream>
using namespace std;

int main() 
{
    int number, i = 1, factorial = 1;

    cout << "Enter a positive integer: ";
    cin >> number;
    
    while ( i <= number) {
        factorial *= i;      //factorial = factorial * i;
        ++i;
    }

    cout<<"Factorial of "<< number <<" = "<< factorial;
    return 0;
}

Output

Enter a positive integer: 4
Factorial of 4 = 24

In this program, user is asked to enter a positive integer which is stored in variable number. Let's suppose, user entered 4.

Then, the while loop starts executing the code. Here's how while loop works:

1. Initially, i = 1, test expression i <= number is true and factorial becomes 1.

2. Variable i is updated to 2, test expression is true, factorial becomes 2.

3. Variable i is updated to 3, test expression is true, factorial becomes 6.

4. Variable i is updated to 4, test expression is true, factorial becomes 24.

5. Variable i is updated to 5, test expression is false and while loop is terminated.