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DO/WHILE Loops - Advanced

When to Use DO/WHILE Loops

Use DO/WHILE loops when something must run AT LEAST ONCE, then check if it should happen again.

Perfect for: Menus (must show first), validation (must ask once), surveys/forms, registration/booking, any system where first attempt is guaranteed.

Key Difference

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

Example 1: Menu System - Always Show Menu First

Click to view code 
int menuChoice;

do
{
    Console.WriteLine("--- CAFE MENU ---");
    Console.WriteLine("1. Order Coffee");
    Console.WriteLine("2. View Orders");
    Console.WriteLine("3. Exit");
    Console.Write("Choose option: ");
    menuChoice = int.Parse(Console.ReadLine());

    if (menuChoice == 1)
        Console.WriteLine("Coffee ordered!");
    else if (menuChoice == 2)
        Console.WriteLine("Viewing orders...");

} while (menuChoice != 3);
Console.WriteLine("Goodbye!");

Example 2: Survey - Must Answer At Least One Question

Click to view code 
string answer;

do
{
    Console.Write("Rate our service (1-5): ");
    answer = Console.ReadLine();

    if (answer != "1" && answer != "2" && answer != "3" && answer != "4" && answer != "5")
    {
        Console.WriteLine("Invalid rating!");
    }

} while (answer != "1" && answer != "2" && answer != "3" && answer != "4" && answer != "5");
Console.WriteLine($"Thank you for rating us {answer} stars!");

Example 3: Registration - Must Enter Valid Email

Click to view code 
string email;

do
{
    Console.Write("Enter email address: ");
    email = Console.ReadLine();

    if (!email.Contains("@"))
    {
        Console.WriteLine("Invalid email - must contain @");
    }

} while (!email.Contains("@"));
Console.WriteLine($"Registered: {email}");

Example 4: Gym Booking - Book At Least One Session

Click to view code 
List<string> sessions = new List<string>();
string continueBooking;

do
{
    Console.Write("Enter session time (e.g., 9am): ");
    string session = Console.ReadLine();
    sessions.Add(session);
    Console.WriteLine($"Booked! Total sessions: {sessions.Count}");

    Console.Write("Book another? (y/n): ");
    continueBooking = Console.ReadLine();

} while (continueBooking == "y");
Console.WriteLine($"Booking complete: {sessions.Count} sessions booked");

Example 5: Quiz - Must Answer At Least One Question

Click to view code 
string quizAnswer;
int attempts = 0;

do
{
    attempts++;
    Console.Write("What is 5 + 3? ");
    quizAnswer = Console.ReadLine();

    if (quizAnswer != "8")
    {
        Console.WriteLine($"Wrong! Try again (Attempt {attempts})");
    }

} while (quizAnswer != "8");
Console.WriteLine($"Correct! You got it in {attempts} attempts");

Assessment Use Cases

When to Use in Your Software Module

  • Menu systems (always display menu)
  • Data validation (must prompt user)
  • Registration forms (must collect info)
  • Booking systems (must make at least one booking)
  • Survey/quiz systems (must answer)