Lesson 10: Functions/Methods in C#

Welcome to Lesson 10! In this lesson, we’ll explore functions, also known as methods in C#. Functions are fundamental building blocks in programming that allow you to organize, reuse, and manage your code efficiently. We’ll cover how to define, call, and work with functions in C#.

1. What is a Function/Method?

A function (or method) is a reusable block of code that performs a specific task. Functions help you avoid code duplication and make your program easier to maintain and understand. In C#, functions are referred to as methods when they are part of a class.

2. Defining a Method

To define a method, you specify its return type, name, parameters (if any), and the body of the method. The return type indicates what type of value the method will return. If the method doesn’t return a value, the return type is void.

Syntax:

returnType MethodName(parameters)
{
    // Method body
    return returnValue; // Optional, if returnType is not void
}

Example:

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

Explanation:

• int is the return type.
• Add is the method name.
• (int a, int b) are the parameters.
• return a + b; returns the sum of a and b.

3. Calling a Method

To use a method, you call it by its name and provide the necessary arguments.

Example:

int result = Add(5, 3);
Console.WriteLine(result); // Output: 8

Explanation:

• The Add method is called with arguments 5 and 3, and the result is stored in result.

4. Methods with No Return Value

If a method does not return a value, use void as the return type.

Example:

void PrintMessage(string message)
{
    Console.WriteLine(message);
}

Calling the Method:

PrintMessage("Hello, world!"); // Output: Hello, world!

Explanation:

• PrintMessage prints the provided message to the console and does not return a value.

5. Method Overloading

Method overloading allows you to define multiple methods with the same name but different parameters. C# distinguishes overloaded methods by their parameter lists.

Example:

int Multiply(int a, int b)
{
    return a * b;
}

double Multiply(double a, double b)
{
    return a * b;
}

Explanation:

• Two Multiply methods are defined: one for integers and one for doubles. C# determines which method to call based on the argument types.

6. Optional Parameters

You can specify default values for parameters, making them optional when calling the method.

Example:

void Greet(string name, string greeting = "Hello")
{
    Console.WriteLine($"{greeting}, {name}!");
}

Calling the Method:

Greet("Alice");             // Output: Hello, Alice!
Greet("Bob", "Goodbye");   // Output: Goodbye, Bob!

Explanation:

• The greeting parameter has a default value of “Hello”. If no value is provided, the default is used.

7. Return Statements

The return statement is used to return a value from a method. If the return type is void, you use return to exit the method early.

Example:

int Square(int number)
{
    return number * number;
}

void PrintSquare(int number)
{
    int result = Square(number);
    Console.WriteLine(result);
}

Explanation:

• The Square method returns the square of a number.
• The PrintSquare method calls Square and prints the result.

8. Passing Parameters by Reference

Parameters can be passed by reference using the ref or out keywords, allowing methods to modify the original variables.

Example Using ref:

void Increment(ref int number)
{
    number++;
}

int value = 5;
Increment(ref value);
Console.WriteLine(value); // Output: 6

Explanation:

• The Increment method modifies the value variable directly because it is passed by reference using ref.

9. Methods with out Parameters

The out keyword allows a method to return multiple values by modifying variables passed as arguments.

Example:

void Divide(int dividend, int divisor, out int quotient, out int remainder)
{
    quotient = dividend / divisor;
    remainder = dividend % divisor;
}

int q, r;
Divide(10, 3, out q, out r);
Console.WriteLine($"Quotient: {q}, Remainder: {r}"); // Output: Quotient: 3, Remainder: 1

Explanation:

• The Divide method calculates both the quotient and remainder, which are returned using out parameters.

10. Example: Calculating Factorial

Let’s create a method to calculate the factorial of a number using recursion.

Example:

int Factorial(int n)
{
    if (n <= 1)
        return 1;
    else
        return n * Factorial(n - 1);
}

Console.WriteLine(Factorial(5)); // Output: 120

Explanation:

• The Factorial method calls itself recursively to compute the factorial of a number.

Summary

In this lesson, you learned about functions (methods) in C#, including how to define, call, and work with them. We covered different aspects such as method overloading, optional parameters, passing parameters by reference, and returning multiple values. Methods are essential for writing clean, reusable, and organized code.

Happy coding!