Return values and void methods in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C# code with return values?

Look at this code. What will it print when run?

C Sharp (C#)

using System;
class Program {
    static int MultiplyByTwo(int x) {
        return x * 2;
    }
    static void Main() {
        int result = MultiplyByTwo(5);
        Console.WriteLine(result);
    }
}

A 10

B 5

C 0

D Nothing, it causes a compile error

💡 Hint

The method MultiplyByTwo returns the input number multiplied by 2.

The method MultiplyByTwo returns 5 * 2 = 10. The Main method prints this value.

❓ Predict Output

intermediate

What will this void method print?

Check this code. What does it print when run?

C Sharp (C#)

using System;
class Program {
    static void PrintMessage() {
        Console.WriteLine("Hello World");
    }
    static void Main() {
        PrintMessage();
    }
}

A Hello World

B Compile error because void methods cannot be called

C HelloWorld (without space)

D Nothing, because void methods don't print

💡 Hint

Void methods can print to the screen using Console.WriteLine.

The method PrintMessage prints "Hello World". Void means it returns no value but can still print.

❓ Predict Output

advanced

What is the output of this method returning a string?

What does this program print when run?

C Sharp (C#)

using System;
class Program {
    static string GetGreeting(string name) {
        return $"Hi, {name}!";
    }
    static void Main() {
        string greet = GetGreeting("Anna");
        Console.WriteLine(greet);
    }
}

A Hi Anna!

B Hi, Anna!

C Hi, {name}!

D Compile error due to string interpolation

💡 Hint

The method uses string interpolation to insert the name.

The method returns the string with the name inserted using $"..." syntax. It prints "Hi, Anna!".

❓ Predict Output

advanced

What happens if you try to return a value from a void method?

Look at this code. What error will it cause?

C Sharp (C#)

using System;
class Program {
    static void DoSomething() {
        return 5;
    }
    static void Main() {
        DoSomething();
    }
}

A No error, returns 5 silently

B Prints 5

C Runtime error

D Compile error: Cannot return a value from a method with void return type

💡 Hint

Void methods cannot return any value.

The method DoSomething is declared void but tries to return 5, which is not allowed and causes a compile error.

🧠 Conceptual

expert

How many items are in the list after this method runs?

Consider this code. How many items does the list contain after Main runs?

C Sharp (C#)

using System;
using System.Collections.Generic;
class Program {
    static List<int> AddNumbers() {
        var list = new List<int>();
        for (int i = 0; i < 3; i++) {
            list.Add(i);
        }
        return list;
    }
    static void Main() {
        var numbers = AddNumbers();
        numbers.Add(3);
        Console.WriteLine(numbers.Count);
    }
}

A 0

B 3

C 4

D Compile error

💡 Hint

The method adds 3 items, then Main adds one more.

AddNumbers creates a list with 3 items (0,1,2). Main adds one more item (3). Total is 4.