C++ While Loop Control Structure

Introduction

The while loop in C++ is used when the number of iterations is not known in advance. It keeps executing a block of code as long as the given condition is true. This makes it ideal for cases where you want to loop until a specific event occurs (like user input, reaching a target, or waiting for a condition).

Syntax

while (condition) {
    // statements
}

while (condition) {
    // statements
}

• condition: evaluated before each iteration.
• If condition is true → body executes.
• If condition is false → loop stops immediately.

Working of While Loop

1. Test the condition.
2. If true → run loop body → go back to step 1.
3. If false → exit loop.

Example: Print numbers 1 to 5 using While Loop

#include <iostream>
using namespace std;

int main() {
    int i = 1;
    while (i <= 5) {
        cout << i << " ";
        i++;
    }
    return 0;
}

#include <iostream>
using namespace std;

int main() {
    int i = 1;
    while (i <= 5) {
        cout << i << " ";
        i++;
    }
    return 0;
}

Output:

1 2 3 4 5

1 2 3 4 5

Key Points

• Entry-controlled loop → condition is checked first, so loop may run 0 times if condition is false initially.
• Ideal when the stopping condition is not known in advance.

Common Uses

• Reading input until a sentinel value (e.g., until user enters 0).
• Loops where iterations depend on calculations instead of fixed count.

Tips

• Always ensure your condition eventually becomes false (otherwise infinite loop).
• Use break carefully if you need to exit earlier.