In .NET, Function Overloading and Function Overriding are both forms of Polymorphism, but they work very differently.

🔹 Function Overloading vs Function Overriding

Feature	Function Overloading	Function Overriding
Definition	Same method name with different parameters	Child class redefines parent class method
Occurs in	Same class	Base class + Derived class
Parameters	Must be different	Must be same
Return type	Can be different (but not only difference)	Must be same (or covariant)
Keywords	No special keyword needed	virtual, override, abstract
Polymorphism Type	Compile-time polymorphism	Runtime polymorphism
Inheritance Required	❌ No	✅ Yes

🔹 Function Overloading Example

Same method name, different parameters.

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

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

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

Usage

Calculator calc = new Calculator();

calc.Add(2,3);       // Calls first method
calc.Add(2,3,4);     // Calls second method
calc.Add(2.5,3.5);   // Calls third method

👉 Same method name Add, different parameters
👉 This is Function Overloading

🔹 Function Overriding Example

Parent class method overridden in child class.

public class Animal
{
    public virtual void Speak()
    {
        Console.WriteLine("Animal speaks");
    }
}

public class Dog : Animal
{
    public override void Speak()
    {
        Console.WriteLine("Dog barks");
    }
}

Usage

Animal animal = new Dog();
animal.Speak();

Output

Dog barks

👉 Parent method replaced by child method
👉 This is Function Overriding

🔹 Keywords Used in Overriding

Keyword	Purpose
virtual	Allows method to be overridden
override	Overrides base method
abstract	Must be overridden
sealed	Prevents further overriding

🔹 Abstract Example

public abstract class Animal
{
    public abstract void Speak();
}

public class Dog : Animal
{
    public override void Speak()
    {
        Console.WriteLine("Dog barks");
    }
}

🔹 Interview One-Line Answer 

Function Overloading → Same method name, different parameters (Compile time)

Function Overriding → Child class modifies parent class method (Runtime)

🔹 Real-World Example

Overloading

Login(username, password)
Login(googleToken)
Login(mobileOtp)

Overriding

Employee.CalculateSalary()

Manager.CalculateSalary()   // Different logic
Developer.CalculateSalary() // Different logic

🔹 Interview Trick Question ⚡

Can we override static method?

❌ No — Static methods cannot be overridden

🔹 Another Trick Question

Can we overload static method?

✅ Yes — Static methods can be overloaded