Module 2: Your First yield return

Practice Tasks

Complete these tasks to reinforce what you learned in this module.

Task 1: Rewrite the countdown

Replace the whole hand-written class with a single iterator method. Countdown(5) should produce 5, 4, 3, 2, 1.

Expected Output:

Five numbers counting down, one per line.

Hint: A for loop stepping down, with yield return i; inside it. The return type is IEnumerable<int>.

Starter Code:

task.cs

using System;
using System.Collections.Generic;

class Program
{
    // Make this an iterator that counts down to 1
    static IEnumerable<int> Countdown(int from)
    {
        yield break;
    }

    static void Main()
    {
        foreach (var n in Countdown(5))
        {
            Console.WriteLine(n);
        }
    }
}

Task 2: Stop at the first blank line

Yield each line, trimmed, until you meet a blank one — then stop, ignoring everything after it. Use yield break.

Expected Output:

Only the lines before the blank one, trimmed.

Hint: string.IsNullOrWhiteSpace(line) tells you when to yield break.

Starter Code:

task.cs

using System;
using System.Collections.Generic;

class Program
{
    static IEnumerable<string> UntilBlank(string[] lines)
    {
        foreach (var line in lines)
        {
            // Stop completely at the first blank line,
            // otherwise hand back the trimmed line
        }

        yield break;
    }

    static void Main()
    {
        var lines = new string[] { "  alpha ", "beta", "   ", "gamma" };

        foreach (var line in UntilBlank(lines))
        {
            Console.WriteLine(line);
        }
    }
}