Method declaration and calling in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a method in C#?

A method is a block of code that performs a specific task. It can be called to run that task whenever needed.

beginner

How do you declare a method that returns no value in C#?

Use the void keyword before the method name. For example:

void SayHello() { Console.WriteLine("Hello!"); }

beginner

How do you call a method named Greet in C#?

Simply write the method name followed by parentheses:

Greet();

beginner

What is the purpose of method parameters?

Parameters let you send information into a method so it can use that data to do its job.

beginner

How do you declare a method that returns an integer value?

Specify the return type before the method name. For example:

int GetNumber() { return 5; }

Which keyword is used to declare a method that does not return any value?

A null

B int

C return

D void

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

How do you call a method named DisplayMessage?

A DisplayMessage;

B DisplayMessage();

C method DisplayMessage();

D call DisplayMessage;

To call a method, write its name followed by parentheses.

What does a method parameter do?

A Sends data into the method

B Returns data from the method

C Stops the method

D Names the method

Parameters allow you to send information into a method.

Which part of a method declaration specifies the type of value it returns?

A Return type before the method name

B Method name

C Parameters inside parentheses

D Method body inside braces

The return type is written before the method name to show what type of value the method returns.

What happens if a method has a return type other than void?

A It cannot be called

B It cannot have parameters

C It must return a value of that type

D It must be static

Methods with a return type other than void must return a value of that type.

Explain how to declare and call a simple method in C# that prints a message.

Think about the method header, body, and how you run it.

Describe the role of parameters and return types in methods.

Consider how methods communicate with the outside.

Practice

1. What is the correct way to declare a method named Greet that returns nothing and takes no parameters in C#?

easy

A. public Greet() void { }

B. void Greet[] { }

C. void Greet { }

D. public void Greet() { }

Solution

1. Step 1: Understand method declaration syntax

   A method declaration starts with an access modifier (like public), then the return type (void means no return), then the method name, and parentheses for parameters.

2. Step 2: Check each option's syntax

   public void Greet() { } correctly uses 'public void Greet() { }'. Options A, B, and D have syntax errors like wrong brackets or missing parentheses.

3. Final Answer:

   public void Greet() { } -> Option D

4. Quick Check:

   Method declaration = public void Greet() { } [OK]

Hint: Method syntax: access + return type + name + parentheses [OK]

Common Mistakes:

• Using square brackets [] instead of parentheses ()
• Omitting parentheses after method name
• Placing return type after method name

2. Which of the following is the correct way to call a method named CalculateSum that takes two integers as parameters?

easy

A. CalculateSum 5, 10;

B. CalculateSum[5, 10];

C. CalculateSum(5, 10);

D. CalculateSum{5, 10};

Solution

1. Step 1: Recall method call syntax

   To call a method, use its name followed by parentheses containing arguments separated by commas.

2. Step 2: Evaluate each option

   CalculateSum(5, 10); uses parentheses correctly. Options B, C, and D use incorrect brackets or omit parentheses, causing syntax errors.

3. Final Answer:

   CalculateSum(5, 10); -> Option C

4. Quick Check:

   Method call = name + parentheses + arguments [OK]

Hint: Call methods with parentheses and comma-separated arguments [OK]

Common Mistakes:

• Using square brackets instead of parentheses
• Omitting parentheses when calling methods
• Using curly braces for method calls

3. What will be the output of the following C# code?

public class Program {
  public static int Double(int x) {
    return x * 2;
  }
  public static void Main() {
    int result = Double(4);
    Console.WriteLine(result);
  }
}

medium

A. 8

B. 4

C. 16

D. Compilation error

Solution

1. Step 1: Understand the method Double

   The method takes an integer x and returns x multiplied by 2.

2. Step 2: Trace the method call in Main

   Double(4) returns 4 * 2 = 8, which is stored in result and printed.

3. Final Answer:

   8 -> Option A

4. Quick Check:

   Double(4) = 8 [OK]

Hint: Multiply input by 2, then print result [OK]

Common Mistakes:

• Confusing return value with input
• Expecting 16 by squaring instead of doubling
• Thinking method does not return a value

4. Identify the error in the following method declaration and fix it:

public int AddNumbers(int a, int b) {
  int sum = a + b;
}

medium

A. Add a return statement: return sum;

B. Change method return type to void

C. Remove parameters from method

D. Add semicolon after method name

Solution

1. Step 1: Check method return type and body

   The method declares it returns an int but does not return any value.

2. Step 2: Fix by adding a return statement

   Adding return sum; returns the calculated value, matching the return type.

3. Final Answer:

   Add a return statement: return sum; -> Option A

4. Quick Check:

   Return value needed for non-void methods [OK]

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

Common Mistakes:

• Forgetting to return a value in non-void methods
• Changing return type incorrectly
• Removing parameters unnecessarily

5. You want to create a method IsEven that returns true if a number is even, otherwise false. Which of the following is the correct method declaration and call to check if 7 is even?

hard

A. public bool IsEven(int num) { if(num / 2 == 0) return true; else return false; } ... bool result = IsEven(7);

B. public bool IsEven(int num) { return num % 2 == 0; } ... bool result = IsEven(7);

C. public void IsEven(int num) { if(num % 2 == 0) return true; else return false; } ... bool result = IsEven(7);

D. public int IsEven(int num) { return num % 2; } ... int result = IsEven(7);

Solution

1. Step 1: Check method return type and logic

   Method should return bool and use modulo (%) to check evenness. public bool IsEven(int num) { return num % 2 == 0; } ... bool result = IsEven(7); correctly returns true if remainder is 0.

2. Step 2: Verify method call and variable type

   public bool IsEven(int num) { return num % 2 == 0; } ... bool result = IsEven(7); calls IsEven(7) and stores result in a bool variable, matching the method return type.

3. Final Answer:

   public bool IsEven(int num) { return num % 2 == 0; } ... bool result = IsEven(7); -> Option B

4. Quick Check:

   Use modulo and bool return for even check [OK]

Hint: Use 'return num % 2 == 0;' for even check [OK]

Common Mistakes:

• Using division instead of modulo for even check
• Returning int instead of bool
• Declaring method void but trying to return a value