Method declaration and calling in C Sharp (C#)

Introduction

Methods help you organize your code into small, reusable actions. You declare a method to define what it does, and call it to use it.

When you want to repeat the same task multiple times without rewriting code.

When you want to break a big problem into smaller, easier steps.

When you want to make your code cleaner and easier to read.

When you want to reuse code in different parts of your program.

When you want to test parts of your program separately.

Syntax

C Sharp (C#)

returnType MethodName(parameters) {
    // code to run
}

returnType is the type of value the method gives back (use void if it returns nothing).

parameters are inputs the method can use, separated by commas.

Examples

A method that prints "Hello!" and returns nothing.

C Sharp (C#)

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

A method that adds two numbers and returns the result.

C Sharp (C#)

int Add(int a, int b) {
    return a + b;
}

A method that returns a name as a string.

C Sharp (C#)

string GetName() {
    return "Alice";
}

Sample Program

This program declares two methods: Greet which prints a welcome message, and Multiply which returns the product of two numbers. The Main method calls both methods to show how they work.

C Sharp (C#)

using System;

class Program {
    static void Greet() {
        Console.WriteLine("Welcome to the program!");
    }

    static int Multiply(int x, int y) {
        return x * y;
    }

    static void Main(string[] args) {
        Greet();
        int result = Multiply(4, 5);
        Console.WriteLine($"4 times 5 is {result}");
    }
}

Important Notes

Methods must be declared inside a class in C#.

Use static keyword if you want to call the method without creating an object.

Method names usually start with a capital letter by convention.

Summary

Methods let you group code to do specific tasks.

Declare a method with a return type, name, and optional parameters.

Call a method by its name and provide any needed inputs.

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