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DO/WHILE Loops

When to Use DO/WHILE Loops

Use DO/WHILE loops when something must happen at least once, then check if it should happen again.

Perfect for: Must ask for name, must show menu, must get valid number, must answer question, must enter data.

Key Difference

DO/WHILE always runs AT LEAST ONCE, even if the condition is false from the start!

Example 1: Must Enter Name (Not Empty)

Click to view code 
string name;

do
{
    Console.Write("Enter your name: ");
    name = Console.ReadLine();
} while (string.IsNullOrEmpty(name));

Console.WriteLine($"Hello, {name}!");

Example 2: Must Enter Number Between 1-10

Click to view code 
int num;

do
{
    Console.Write("Enter number (1-10): ");
    num = int.Parse(Console.ReadLine());
} while (num < 1 || num > 10);

Console.WriteLine($"You entered: {num}");

Example 3: Show Menu At Least Once

Click to view code 
int option;

do
{
    Console.WriteLine("1. Start");
    Console.WriteLine("2. Exit");
    Console.Write("Choose: ");
    option = int.Parse(Console.ReadLine());
} while (option != 2);

Console.WriteLine("Goodbye!");

Example 4: Must Answer Yes or No

Click to view code 
string response;

do
{
    Console.Write("Continue? (yes/no): ");
    response = Console.ReadLine();
} while (response != "yes" && response != "no");

Console.WriteLine($"You said: {response}");

Example 5: Must Enter Positive Number

Click to view code 
int amount;

do
{
    Console.Write("Enter positive number: ");
    amount = int.Parse(Console.ReadLine());
} while (amount <= 0);

Console.WriteLine($"Amount: {amount}");

Quick Reference

DO/WHILE Loop Pattern

do
{
    // Do this at least once
} while (condition is true);

Key points:

  • Code runs FIRST, then checks condition
  • Always executes at least once
  • Perfect for validation and menus
  • Don't forget the semicolon after while!