Difference Between a While Loop and a Do-While Loop in C++

1. Introduction

In C++ programming, while and do-while loops are used for executing a block of code repeatedly. While they are similar in many ways, they have a key difference in how they evaluate their condition and when they begin executing the loop body.

2. Key Points

1. A while loop checks its condition before executing the loop body.

2. A do-while loop executes its loop body at least once before checking the condition.

3. In a while loop, the loop body may not execute at all if the condition is false initially.

4. In a do-while loop, the loop body always executes at least once, regardless of the initial condition.

3. Differences

while Loop	do-while Loop
Condition checked before loop body execution.	Loop body executed once before condition check.
May not execute if condition is false initially.	Guaranteed to execute at least once.

4. Example

#include <iostream>
using namespace std;

int main() {
    int count = 5;

    // while loop example
    cout << "while loop output: ";
    while (count < 5) {
        cout << count << " ";
        count++;
    }
    cout << endl;

    // do-while loop example
    cout << "do-while loop output: ";
    count = 5;
    do {
        cout << count << " ";
        count++;
    } while (count < 5);
    cout << endl;

    return 0;
}

Output:

while loop output:
do-while loop output: 5

Explanation:

1. In the while loop example, since count is not less than 5, the loop body does not execute.

2. In the do-while loop example, the loop body executes once before the condition count < 5 is checked.

5. When to use?

- Use a while loop when you want the loop to execute only if the condition is true from the start.

- Use a do-while loop when you need to ensure that the loop body is executed at least once, such as in menus or user input validation.

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