using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("please enter number");

        double x=double.Parse(Console.ReadLine());

        Console.WriteLine("please enter number");

        double y=double.Parse(Console.ReadLine());

        Console.WriteLine("what do you want to do ?");

        string z=Console.ReadLine();

        if (z=="div") Console.WriteLine(x + " / " + y +" = "+(x/y));  

        if (z=="mul") Console.WriteLine(x + " * " + y +" = "+(x*y));  

        if (z=="add") Console.WriteLine(x + " + " + y +" = "+(x+y));  

        if (z=="sub") Console.WriteLine(x + " - " + y +" = "+(x-y));  

    }

}

​