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.

Practice

1. Which statement correctly describes a void method in C#?

easy

A. It does not return any value.

B. It must return an integer value.

C. It always returns a string.

D. It returns a boolean value.

Solution

1. Step 1: Understand the meaning of void in C#

   The keyword void means the method does not return any value.

2. Step 2: Compare with other return types

   Methods with other return types like int, string, or bool must return a value of that type, but void methods do not return anything.

3. Final Answer:

   It does not return any value. -> Option A

4. Quick Check:

   Void means no return value [OK]

Hint: Void means no value comes back from the method [OK]

Common Mistakes:

• Thinking void methods return a default value
• Confusing void with returning null
• Assuming void methods must return something

2. Which of the following is the correct syntax for a method that returns an integer value in C#?

easy

A. public void GetNumber() { return 5; }

B. public void GetNumber() { Console.WriteLine(5); return 5; }

C. public int GetNumber() { Console.WriteLine(5); }

D. public int GetNumber() { return 5; }

Solution

1. Step 1: Identify method return type and return statement

   The method declares int return type, so it must return an integer value using return.

2. Step 2: Check each option for correct syntax

   public int GetNumber() { return 5; } correctly declares int and returns 5. public void GetNumber() { return 5; } is void but tries to return a value (invalid). public int GetNumber() { Console.WriteLine(5); } returns nothing despite int return type. public void GetNumber() { Console.WriteLine(5); return 5; } is void but tries to return a value (invalid).

3. Final Answer:

   public int GetNumber() { return 5; } -> Option D

4. Quick Check:

   Return type matches returned value [OK]

Hint: Return type must match the returned value type [OK]

Common Mistakes:

• Returning a value from a void method
• Not returning a value from a non-void method
• Using Console.WriteLine instead of return

3. What is the output of the following C# code?

public class Program {
  public static int Add(int a, int b) {
    return a + b;
  }
  public static void Main() {
    int result = Add(3, 4);
    Console.WriteLine(result);
  }
}

medium

A. 7

B. 34

C. 0

D. Compile error

Solution

1. Step 1: Understand the Add method

   The method Add takes two integers and returns their sum.

2. Step 2: Trace the Main method execution

   Main calls Add(3, 4), which returns 7. Then it prints 7 to the console.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   3 + 4 = 7 [OK]

Hint: Add returns sum; printed result is sum [OK]

Common Mistakes:

• Concatenating numbers as strings
• Confusing return with print
• Expecting void method to return value

4. Identify the error in this C# method:

public int Multiply(int x, int y) {
  int product = x * y;
}

medium

A. Incorrect method name.

B. Variables cannot be declared inside methods.

C. Missing return statement for non-void method.

D. Method parameters must be strings.

Solution

1. Step 1: Check method return type and body

   The method declares int return type but does not return any value.

2. Step 2: Identify missing return statement

   Since the method is not void, it must have a return statement returning an integer value like return product;.

3. Final Answer:

   Missing return statement for non-void method. -> Option C

4. Quick Check:

   Non-void methods must return a value [OK]

Hint: Non-void methods must always return a value [OK]

Common Mistakes:

• Forgetting to return a value in non-void methods
• Thinking variable declaration is invalid inside methods
• Assuming parameters must be strings

5. You want to create a method that prints a greeting message but does not return any value. Which method signature and body is correct in C#?

hard

A. public string Greet() { Console.WriteLine("Hello!"); return "Hello!"; }

B. public void Greet() { Console.WriteLine("Hello!"); }

C. public void Greet() { return "Hello!"; }

D. public string Greet() { Console.WriteLine("Hello!"); }

Solution

1. Step 1: Understand method purpose and return type

   The method should print a message and not return any value, so it should be void.

2. Step 2: Check each option for correctness

   public void Greet() { Console.WriteLine("Hello!"); } correctly uses void and prints the message without returning anything. public string Greet() { Console.WriteLine("Hello!"); return "Hello!"; } returns a string, which is not needed. public void Greet() { return "Hello!"; } tries to return a string in a void method (invalid). public string Greet() { Console.WriteLine("Hello!"); } declares string return type but does not return anything (invalid).

3. Final Answer:

   public void Greet() { Console.WriteLine("Hello!"); } -> Option B

4. Quick Check:

   Void method prints only, no return [OK]

Hint: Void methods do actions, no return needed [OK]

Common Mistakes:

• Returning a value from a void method
• Declaring return type but not returning
• Confusing printing with returning