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C++ While Loop - GeeksforGeeks

Last Updated : 12 Dec, 2024

In C++, the while loop is an entry-controlled loop that repeatedly executes a block of code as long as the given condition remains true. Unlike the for loop, while loop is used in situations where we do not know the exact number of iterations of the loop beforehand as the loop execution is terminated on the basis of the test condition.

Let's take a look at an example:

#include <iostream>
using namespace std;

int main() {
  
  	// while loop to print numbers from 1 to 5
    int i = 0;
    while (i < 5) {
        cout << "Hi" << endl;
        i++;
    }

    return 0;
}

Explanation: The above loop prints the text "Hi" till the given condition is true i.e. i is less than 5. In each execution of the loop's statement, it increments i till i is less than 5.

while (condition) {
// Body of the loop
update expression
}

Though the above is the formal syntax of the while loop, we need to declare the loop variable beforehand and update it in the body of the loop. The various parts of the While loop are:

1. Condition: The loop executes its body till this condition remains true.
2. Update Expression: Update the value of loop variable to make it closer to the termination condition.
3. Body: It is a group of statement that will be executed till the condition remains true.

The working of the while loop can be understood using the above image:

1. Control falls into the while loop.
2. The flow jumps to Condition
3. Condition is tested.
   • If the Condition yields true, the flow goes into the Body.
   • If the Condition yields false, the flow goes outside the loop
4. The statements inside the body of the loop get executed.
5. Updation takes place.
6. Control flows back to Step 2.
7. The while loop has ended, and the flow has gone outside.

The below examples demonstrate how to use while loop in our C++ programs:

#include <bits/stdc++.h>
using namespace std;

int main() {
  
  	// Declaration and Initialization of loop variable
    int i = 1; 

    // while loop to print numbers from 1 to 5
    while (i <= 5) {
        cout << i << " ";
      
      	// Updating loop varialbe
        i++;
    }

    return 0;
}

#include <iostream>
using namespace std;

int main() {
    int n = 5;

    int sum = 0;

    // while loop to calculate the sum
    while (n > 0) {
        sum += n;
        n--;
    }

    cout << sum;
    return 0;
}

Just like other loops, we can also nest one while loop into another while loop.

#include <iostream>
using namespace std;

int main()
{
    int i = 0;

    // Outer loop to print each row
    while (i < 4) {
        int j = 0;
      
        // Inner loop to print each character
        // in each row
        while (j < 4) {
            cout << "* ";
            j++;
        }
        cout << endl;
        i++;
    }

    return 0;
}

* * * * 
* * * * 
* * * * 
* * * * 

We can create an infinite loop using a while loop by defining a condition that is always true.

#include <iostream>
using namespace std;

int main() {
  
  	// Infinite loop
    while (true) {
        cout << "gfg" << endl;
    }

    return 0;
}

Output

gfg
gfg
.
.
.
infinite times

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