Return values and void methods in C Sharp (C#) - Mini Project: Build & Apply

Return values and void methods

📖 Scenario: You are creating a simple calculator program that can add two numbers and also print a greeting message.

🎯 Goal: Build a program with one method that returns the sum of two numbers and another method that prints a greeting message without returning anything.

📋 What You'll Learn

Create a method called AddNumbers that takes two integers and returns their sum.

Create a method called PrintGreeting that prints a greeting message and returns nothing (void).

Call both methods from the Main method and display the sum.

💡 Why This Matters

🌍 Real World

Methods that return values and void methods are common in all software programs to organize code and perform tasks.

💼 Career

Understanding how to write and use methods is essential for any programming job, as it helps create reusable and clear code.

1

Create the AddNumbers method

Create a method called AddNumbers that takes two integers named num1 and num2 and returns their sum as an integer.

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
    }

    // Your code here
}

Hint

Use static int AddNumbers(int num1, int num2) and return the sum with return num1 + num2;.

2

Create the PrintGreeting method

Create a method called PrintGreeting that prints the message "Hello, welcome to the calculator!" and returns nothing (void).

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
    }

    static int AddNumbers(int num1, int num2)
    {
        return num1 + num2;
    }

    // Your code here
}

Hint

Use static void PrintGreeting() and inside it use Console.WriteLine to print the greeting.

3

Call both methods in Main

Inside the Main method, call PrintGreeting() first, then call AddNumbers with 5 and 7 as arguments and store the result in an integer variable called sum.

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
        // Your code here
    }

    static int AddNumbers(int num1, int num2)
    {
        return num1 + num2;
    }

    static void PrintGreeting()
    {
        Console.WriteLine("Hello, welcome to the calculator!");
    }
}

Hint

Call PrintGreeting() and then call AddNumbers(5, 7) storing the result in sum.

4

Print the sum result

Add a line in the Main method to print the text "Sum: " followed by the value of the sum variable.

C Sharp (C#)

using System;

class Program
{
    static void Main()
    {
        PrintGreeting();
        int sum = AddNumbers(5, 7);
        // Your code here
    }

    static int AddNumbers(int num1, int num2)
    {
        return num1 + num2;
    }

    static void PrintGreeting()
    {
        Console.WriteLine("Hello, welcome to the calculator!");
    }
}

Hint

Use Console.WriteLine("Sum: " + sum); to print the sum.

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