C++ | C Plus Plus While loop

In this article, we will discuss the C++ while loop with its syntax, use, key features, key points, pseudo code, and examples.

What is the While Loop?

The “while loop” is a control flow statement that enables code to run repeatedly in response to a specified condition. The while loop is an iterative control statement. A while loop repeatedly executes loop’s statement(s) several times, as a given condition is true. Execution of the loop is terminated when the condition of the while loop becomes false and executes code after the loop.

Syntax:

It has the following syntax:

while (condition) {

    // Code to be executed

}

Explanation:

• Condition: A boolean statement that determines whether the loop continues or stops.
• The loop keeps going as long as the condition is true.
• If the condition is found to be false, the loop ends.

Working Process of While Loop:

• While the loop first checks, the condition is applied.
• If the condition of a while loop is satisfied (true), statement(s) within the loop is executed. If the condition of a while loop is not satisfied (false), program execution is terminated from the loop and a statement after the loop is executed.
• Repeatedly check the loop condition and execute according to step 2.

Key features:

Several key features of the while loop in C++ are as follows:

1. Entry-Controlled Loop:

Before the body of the loop is executed, the condition is examined.
The loop never runs if the condition is originally false.

2. The process continues until the condition is no longer met.

The loop keeps running once the condition is met.

3. This technique is applied when the number of iterations is unknown.

The while loop is utilized when we are unsure of the number of times it should run, compared to the for loop, which is employed when the number of iterations is known.

4. Loop Control Variable Must Be Updated Manually

In order to prevent endless loops, we must update the condition variable inside the loop (for example, by increasing a counter).

5. If a condition is not updated correctly, it may result in endless loops.

An endless loop could result from the condition never becoming false if the loop control variable is left unaltered inside the loop.

6. It is Compatible with Any Condition.

The condition may entail logical operations (&&, ||), comparisons (<, >, ==), or even function return values.

7. Suitable for a Range of Uses

It is useful for continuing a program until an exit condition is satisfied, reading files line by line, verifying user input, and more.

Pseudo code:

START

    Initialize a variable (e.g., count = 1)

   

    WHILE (condition is true)  // Example: count <= 5

        PRINT "Count: " and the current value of count

        Increment count by 1

    END WHILE


STOP

Algorithm:

• Start the program.

• Initialize a variable (e.g., count = 1).

• Check the condition (count <= 5).

• If the condition is true, proceed to step 4.

• If the condition is false, go to step 6.

• Execute the loop body:      

• Print the current value of count.

• Increment count by 1.

• Repeat step 3 until the condition becomes false.

• Stop the program.

Example 1:

Let us take an example to illustrate the while loop in C++.

#include <iostream>

using namespace std;


int main() {

    int count = 1;


    while (count <= 5) {  // Loop runs while count is ≤ 5

        cout << "Count: " << count << endl;

        count++;  // Increment count

    }


    return 0;

}

Output:

Count: 1

Count: 2

Count: 3

Count: 4

Count: 5

Key points:

• The condition is evaluated before to the loop’s body being run.
• If the condition is false from the start, the loop doesn’t execute at all.
• Make sure the loop has an exit condition at all times to prevent an unending loop.

Pseudo code for above example code:

For count = 1, while (count <= 5):

Iteration 1 → Print Count: 1, count = 2

Iteration 2 → Print Count: 2, count = 3

Iteration 3 → Print Count: 3, count = 4

Iteration 4 → Print Count: 4, count = 5

Iteration 5 → Print Count: 5, count = 6

Condition count <= 5 is now false, so loop stops.

Infinite loop Example:

while (true) {  // This loop will run forever

    cout << "This is an infinite loop!" << endl;

}

Example 2:

Let us take another example to illustrate the while loop in C++.

#include <iostream>

using namespace std;

int main()

{

    int n, sum = 0, i = 1;

    cout << "Enter a positive number: ";

    cin >> n;

    while (i <= n) {  // Loop runs until i is greater than n

        sum += i;  // Add i to sum

        i++;  // Increment i

    }

    cout << "Sum of first " << n << " natural numbers is: " << sum << endl;

    return 0;

}

Output:

Enter a positive number: 5

Sum of first 5 natural numbers is: 15

Explanation:

• The user enters n.
• Every number is added to the sum in a while loop that runs from 1 to n.
• When i > n, the loop ends, and the total is shown.

Conclusion:

In conclusion, the simplest while loop structure in C++ is a way of executing a block of statements repeatedly based on a certain condition. Since it is an entry-controlled loop, the condition has to be checked before the execution of the loop body; hence, it is suitable for cases where the number of iterations beforehand is not known. The loop control variable should be properly used to prevent an infinite loop and allow the program to run smoothly without any interruptions. Input validation, calculations that need repetition, and auto processes are examples that use the while loop commonly. Developers can create efficient, faultless looping constructs by understanding C++ best practices and features.