Return values and void methods in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a return value in a method?

A return value is the result a method sends back to the part of the program that called it. It can be a number, text, or any data type.

beginner

What does a void method mean in C#?

A void method does not return any value. It just runs some code and finishes without sending anything back.

beginner

How do you return a value from a method in C#?

Use the return keyword followed by the value you want to send back. For example: return 5;

intermediate

Can a method have both void and return a value?

No. A method declared as void cannot return a value. If it returns a value, it must have a matching return type.

intermediate

What happens if a method with a return type does not have a return statement?

The program will give a compile-time error because it expects a value to be returned from the method.

What keyword do you use to send a value back from a method?

A return

B send

C output

D yield

The return keyword is used to send a value back from a method.

What type of method does NOT return any value?

A bool

B string

C int

D void

A void method does not return any value.

Which of these is a valid method header for a method that returns a number?

A int GetNumber()

B void GetNumber()

C void GetNumber(int number)

D string GetNumber()

The method int GetNumber() returns an integer number.

What will happen if a method declared to return int does not have a return statement?

A It will return 0 automatically

B It will cause a compile-time error

C It will return null

D It will run but return garbage value

Methods with a return type must have a return statement; otherwise, the compiler shows an error.

Can a void method use the return keyword?

A No, never

B Yes, with a value

C Yes, but only without a value

D Only in constructors

A void method can use return; to exit early but cannot return a value.

Explain the difference between a method that returns a value and a void method.

Think about whether the method sends something back or just runs code.

Describe what happens if you forget to include a return statement in a method that should return a value.

What does the compiler expect from methods with return types?

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