C# Do While loop

The do-while loop in C# is a control flow statement that executes a block of code at least once and then repeats the loop as long as a specified condition evaluates to true. It is similar to the while loop, but the key difference is that the condition is evaluated after the execution of the loop body, not before. Therefore, the body of the loop is guaranteed to execute at least once, even if the condition is initially false.

The do-while loop is similar to the while loop, but it checks the condition after each execution of its loop body. This type of loop is called a loop with a condition at the end (post-test loop). A do-while loop looks like this

The do-while loop is used when we want to guarantee that the sequence of operations in it will be executed repeatedly and at least once at the beginning of the loop.

Syntax:


do
{
    // Code to be executed
} while (condition);

Explanation:

condition: This is a boolean expression that will be evaluated after each iteration of the loop. If the condition is true, the loop will continue. If the condition is false, the loop will terminate.

Note:

The body of the loop is executed at least once regardless of the condition, because the condition is checked after the first iteration.
If the condition is true, the loop continues to execute; if false, the loop ends.

Example:


using System;

class ProgramExample
{
    static void Main()
    {
        int count = 1;
        // do-while loop
        do
        {
            Console.WriteLine("number: " + count);
            count++;  // Increment the counter
        }
        while (count <= 5);
    }
}

Output:

number: 1
number: 2
number: 3
number: 4
number: 5

Example: If we define count > 5 in the while loop then it will execute only one time.


using System;

class ProgramExample
{
    static void Main()
    {
        int count = 1;
        
        // do-while loop
        do
        {
            Console.WriteLine("number: " + count);
            count++;  // Increment the counter
        }
        while (count > 5);
    }
}

Output:

number: 1

C# Do While loop – Interview Questions

Q 1: What is a do-while loop?

Ans: It executes code at least once before checking the condition.

Q 2: Key difference between while and do-while?

Ans: Do-while executes at least once; while may not.

Q 3: When is do-while loop used?

Ans: When code must run at least once.

Q 4: Does do-while require semicolon?

Ans: Yes, after the while condition.

Q 5: Can do-while be nested?

Ans: Yes.