using System;

public class Calculator

{

    static public void Main ()

    {

        Console.WriteLine("Tinh?\n1/ Phep cong\n2/ Phep tru\n3/ Phep nhan\n4/ Phep chia"); //Calculate? 1/ a + b 2/ a - b 3/ a * b 4/ a / b

   int input = Convert.ToInt32(Console.ReadLine());

   bool done = false;

    if (input > 0 && input <= 4)

    {

     Console.WriteLine("Nhap gia tri cua a: "); //type in the value of a

    double a = Convert.ToDouble(Console.ReadLine());

    Console.WriteLine("Nhap gia tri cua b: "); //type in the value of b

    double b = Convert.ToDouble(Console.ReadLine());

    switch(input)

    {

     case 1:

     double tong = a + b; Console.WriteLine("Tong cua a va b la: "+ tong +"\nPress any key to continue"); //a + b =

        Console.ReadKey();

     break;

     case 2:

     double hieu = a - b;

     Console.WriteLine("Hieu cua a va b la: "+ hieu +"\nPress any key to contiunue"); //a - b =

     Console.ReadKey();

     break;

     case 3:

     double tich = a * b;

     Console.WriteLine("Tich cua a va b la: "+ tich +"\nPress any key to continue"); //a * b =

     Console.ReadKey();

     break;

     case 4:

     double thuong = a / b;

     Console.WriteLine("Thuong cua a va b la: "+ thuong +"\nPress any key to continue");//a / b = 

     Console.ReadKey();

     break;

    }

    }

    else

    {

         Console.WriteLine("Invalid input please restart");

      Console.ReadKey();

    }

    }

}