While Loop in C++.

Loops are used in programming to repeat a specific block of code. In this article, you will learn to create while and do...while loops in C++ programming.

C++ while Loop

The syntax of a while loop is:

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

While loop in C++

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

#include <iostream.h>
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;
}

Expected 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:
• Initially, i = 1, test expression i <= number is true and factorial becomes 1.
• Variable i is updated to 2, test expression is true, factorial becomes 2.
• Variable i is updated to 3, test expression is true, factorial becomes 6.
• Variable i is updated to 4, test expression is true, factorial becomes 24.
• Variable i is updated to 5, test expression is false and while loop is terminated.