C# | Method Overloading

Method Overloading is the common way of implementing polymorphism. It is the ability to redefine a function in more than one form. A user can implement function overloading by defining two or more functions in a class sharing the same name. C# can distinguish the methods with different method signatures. i.e. the methods can have the same name but with different parameters list (i.e. the number of the parameters, order of the parameters, and data types of the parameters) within the same class. 

• Overloaded methods are differentiated based on the number and type of the parameters passed as arguments to the methods.
• You can not define more than one method with the same name, Order and the type of the arguments. It would be compiler error.
• The compiler does not consider the return type while differentiating the overloaded method. But you cannot declare two methods with the same signature and different return type. It will throw a compile-time error. If both methods have the same parameter types, but different return type, then it is not possible.

Why do we need Method Overloading?

If we need to do the same kind of the operation in different ways i.e. for different inputs. In the example described below, we are doing the addition operation for different inputs. It is hard to find many different meaningful names for single action.

Different ways of doing overloading methods- 
Method overloading can be done by changing:  

1. The number of parameters in two methods.
2. The data types of the parameters of methods.
3. The Order of the parameters of methods.

By changing the Number of Parameters

C#

// C# program to demonstrate the function
// overloading by changing the Number
// of parameters
using System;
class GFG {

    // adding two integer values.
    public int Add(int a, int b)
    {
        int sum = a + b;
        return sum;
    }

    // adding three integer values.
    public int Add(int a, int b, int c)
    {
        int sum = a + b + c;
        return sum;
    }

    // Main Method
    public static void Main(String[] args)
    {

        // Creating Object
        GFG ob = new GFG();

        int sum1 = ob.Add(1, 2);
        Console.WriteLine("sum of the two "
                          + "integer value : " + sum1);

        int sum2 = ob.Add(1, 2, 3);
        Console.WriteLine("sum of the three "
                          + "integer value : " + sum2);
    }
}

Output:

sum of the two integer value : 3
sum of the three integer value : 6

By changing the Data types of the parameters

C#

// C# program to demonstrate the function
// overloading by changing the Data types
//  of the parameters
using System;
class GFG {

    // adding three integer values.
    public int Add(int a, int b, int c)
    {
        int sum = a + b + c;
        return sum;
    }

    // adding three double values.
    public double Add(double a,
                      double b, double c)
    {
        double sum = a + b + c;
        return sum;
    }

    // Main Method
    public static void Main(String[] args)
    {

        // Creating Object
        GFG ob = new GFG();

        int sum2 = ob.Add(1, 2, 3);
        Console.WriteLine("sum of the three "
                          + "integer value : " + sum2);
        double sum3 = ob.Add(1.0, 2.0, 3.0);
        Console.WriteLine("sum of the three "
                          + "double value : " + sum3);
    }
}

Output:

sum of the three integer value : 6
sum of the three double value : 6

By changing the Order of the parameters

C#

// C# program to demonstrate the function
// overloading by changing the
// Order of the parameters
using System;
class GFG {

    // Method
    public void Identity(String name, int id)
    {

        Console.WriteLine("Name1 : " + name + ", "
                        + "Id1 : " + id);
    }

    // Method
    public void Identity(int id, String name)
    {

        Console.WriteLine("Name2 : " + name + ", "
                        + "Id2 : " + id);
    }

    // Main Method
    public static void Main(String[] args)
    {

        // Creating Object
        GFG obj = new GFG();

        obj.Identity("Akku", 1);
        obj.Identity(2, "Abby");
    }
}

Output:

Name1 : Akku, Id1 : 1
Name2 : Abby, Id2 : 2

What happens when method signature is same and the return type is different?
The compiler will give error as the return value alone is not sufficient for the compiler to figure out which function it has to call. Only if both methods have different parameter types (so, they have the different signature), then Method overloading is possible.

Example:

C#

// C# program to show error when method signature
// is the same and the return type is different.
using System;
class GFG {

    // adding two integer value.
    public int Add(int a, int b)
    {

        int sum = a + b;
        return sum;
    }

    // adding three integer value.
    public double Add(int a, int b)
    {
        double sum = a + b + 0.0;
        return sum;
    }

    // Main Method
    public static void Main(String[] args)
    {

        // Creating Object
        GFG ob = new GFG();

        int sum1 = ob.Add(1, 2);
        Console.WriteLine("sum of the two "
                          + "integer value :" + sum1);

        int sum2 = ob.Add(1, 2);
        Console.WriteLine("sum of the three "
                          + "integer value :" + sum2);
    }
}

Compile Time Error:

prog.cs(15,19): error CS0111: A member `GFG.Add(int, int)’ is already defined. Rename this member or use different parameter types 
prog.cs(7,16): (Location of the symbol related to previous error)