while Loop

The while loop is a control structure that allows code to be executed repeatedly as long as a specified condition remains true. It’s useful when the number of iterations isn’t known in advance and is determined at runtime.

Syntax of while

while (condition) {
    // Code to execute as long as the condition is true
}

• condition: An expression that evaluates to true (non-zero) or false (zero).
• Loop Body: Contains the code to execute repeatedly while the condition remains true.

How It Works

1. The condition is evaluated before entering the loop.
2. If the condition is true, the loop body is executed.
3. After the body executes, the condition is evaluated again.
4. The loop continues until the condition becomes false.

Example: Basic while Loop

#include <iostream>
using namespace std;

int main() {
    int count = 1;

    while (count <= 5) {
        cout << "Count is: " << count << endl;
        count++;
    }

    return 0;
}

Output:

Count is: 1
Count is: 2
Count is: 3
Count is: 4
Count is: 5

Infinite Loops

If the condition never becomes false, the loop will run indefinitely. For example:

while (true) {
    cout << "This will run forever!" << endl;
}

To avoid infinite loops:

1. Ensure the condition changes inside the loop.
2. Use a break statement to exit when needed.

Example: User Input

A while loop can be used to repeatedly prompt the user for input:

#include <iostream>
using namespace std;

int main() {
    int number;

    cout << "Enter numbers (enter 0 to stop): ";
    cin >> number;

    while (number != 0) {
        cout << "You entered: " << number << endl;
        cin >> number;
    }

    cout << "Loop ended." << endl;
    return 0;
}

Output:

• Input: 5 7 0

You entered: 5
You entered: 7
Loop ended.

Using a Counter Variable

The while loop is often paired with a counter variable to control iterations:

#include <iostream>
using namespace std;

int main() {
    int counter = 0;

    while (counter < 10) {
        cout << counter << " ";
        counter++;
    }

    return 0;
}

Output:

0 1 2 3 4 5 6 7 8 9

Break and Continue

• break: Exits the loop prematurely.
• continue: Skips the rest of the loop body for the current iteration and proceeds to the next iteration.

Example:

#include <iostream>
using namespace std;

int main() {
    int number = 1;

    while (number <= 10) {
        if (number == 5) {
            cout << "Skipping 5" << endl;
            number++;
            continue;
        }
        cout << number << " ";
        number++;
    }

    return 0;
}

Output:

1 2 3 4 Skipping 5 6 7 8 9 10

Nested while Loops

while loops can be nested to handle multi-dimensional scenarios:

#include <iostream>
using namespace std;

int main() {
    int i = 1;

    while (i <= 3) {
        int j = 1;
        while (j <= 3) {
            cout << "(" << i << ", " << j << ") ";
            j++;
        }
        cout << endl;
        i++;
    }

    return 0;
}

Output:

(1, 1) (1, 2) (1, 3)
(2, 1) (2, 2) (2, 3)
(3, 1) (3, 2) (3, 3)

Key Points

1. Use while loops when the number of iterations depends on a condition.
2. Ensure the condition is properly updated to prevent infinite loops.
3. Be cautious with user input to avoid unexpected behavior.