Lesson 14 — Method Overloading in C# (Compile-Time Polymorphism)

Method Overloading is a key part of compile-time polymorphism, one of the two main types of polymorphism in C#.
It allows multiple methods to have the same name but different:

• Number of parameters
• Type of parameters
• Order of parameters

In this lesson, we explore method overloading with clear examples and best practices.

🌟 What is Method Overloading?

✔ Simple Definition:

Method Overloading = Same method name + different parameter list.

The compiler decides at compile time which method to call.

It improves:

• Readability
• Flexibility
• Developer convenience

💡 Why Do We Use Method Overloading?

✔ Makes APIs cleaner

✔ Avoids creating multiple confusing method names

✔ Allows different ways to perform the same operation

✔ Helps in real-world scenarios like Add(), Print(), Draw()

🧱 Basic Example — Add Method

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

    public double Add(double a, double b)
    {
        return a + b;
    }

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

Usage:

Calculator calc = new Calculator();

Console.WriteLine(calc.Add(2, 3));
Console.WriteLine(calc.Add(2.5, 3.5));
Console.WriteLine(calc.Add(5, 6, 7));

✔ Same name: Add
✔ Different parameters
✔ Compiler selects the correct method

🔄 Different Ways to Overload Methods

1️⃣ Changing Number of Parameters

void Print(string name) { }
void Print(string name, int age) { }

2️⃣ Changing Data Types of Parameters

void Draw(int radius) { }
void Draw(double radius) { }

3️⃣ Changing Order of Parameters

void Display(string name, int age) { }
void Display(int age, string name) { }

❌ What You Cannot Do

❌ Only changing return type is NOT enough:

int Test() { }
double Test() { }   // ERROR

Return type does NOT matter for overloading.
Parameter list must be different.

🎨 Real-World Analogy

Example: “Book a Ticket”

You can book a ticket using:

• Name only
• Name + Age
• Name + Age + Passport Number
• Name + Age + Destination

Same action → bookTicket()
Different inputs → Overloading

🌈 Practical Example — Logger Class

public class Logger
{
    public void Log(string message)
    {
        Console.WriteLine($"Info: {message}");
    }

    public void Log(string message, int errorCode)
    {
        Console.WriteLine($"Error {errorCode}: {message}");
    }

    public void Log(string message, bool isCritical)
    {
        if (isCritical)
            Console.WriteLine($"CRITICAL: {message}");
        else
            Console.WriteLine($"Log: {message}");
    }
}

🧠 Important Rules of Overloading

🧰 Constructor Overloading

Overloading also applies to constructors.

public class Person
{
    public Person() { }

    public Person(string name) { }

    public Person(string name, int age) { }
}

This helps initialize objects in different ways.

🔍 Overloading vs Overriding (Quick Difference)

📝 Mini Exercise

Create a class MathOperations with overloaded methods:

• Multiply(int, int)
• Multiply(double, double)
• Multiply(int, int, int)

Call each version and print results.

🔍 FAQs

Q1: Can we overload static methods?

Yes, static methods can be overloaded.

Q2: Can we overload methods by changing only the return type?

No, this will cause an error.

Q3: Can two methods have the same name and same parameters?

No, that causes a duplicate method error.

Q4: Is overloading faster than overriding?

Yes, because overloading is resolved at compile-time.

🎉 Conclusion

You now understand:

✔ What method overloading is
✔ Why it is used
✔ Different ways to overload methods
✔ What is not allowed
✔ The difference between overloading and overriding
✔ Practical and real-world examples

Method overloading is extremely powerful and makes your C# programs flexible and readable.