Classe:
class Calculadora
{
public int Somar(int i1, int i2) => i1 + i2;
public int Somar(int i1, int i2, int i3) => i1 + i2 + i3;
public double Somar(double i1, double i2) => i1 + i2;
}
Program:
Calculadora calc = new Calculadora();
Console.WriteLine(calc.Somar(10, 20));
Console.WriteLine(calc.Somar(5, 10, 15));
Console.WriteLine(calc.Somar(3.5, 2.8));