using System;

public class Program

{

    // a delegate defines the signature of a function:

    // "take two ints as parameters and return one int"

    delegate int Operation (int a, int  b);

    public static void Main()

    {

        Console.WriteLine("Delegate Demo");

        // declare some variables that are of the

        // Operation-delegate-type as lambdas

        Operation 

            add = (a, b) => a + b,

            sub = (a, b) => a - b,

            mul = (a, b) => a * b,

            div = (a, b) => a / b;

        // now we have different operations

        // we can pass around as a variable 

        Console.WriteLine("add: {0}", execute(3, 4, add));

        Console.WriteLine("sub: {0}", execute(3, 4, sub));

        Console.WriteLine("mul: {0}", execute(3, 4, mul));

        Console.WriteLine("div: {0}", execute(8, 4, div));

        Console.WriteLine("square: {0}", execute(2, 3, Square));

    }

    // instead of a lambda, a descrete function can

    // fullfill Operator's signature

    static int Square (int a, int b) => (a*a) + (b*b);

    // this function just executes the delegate

    static int execute (int a, int b, Operation operation) => operation (a, b);

}