static void Main(string[] args)
{
var c = new calc();
System.Console.WriteLine(c.add(2, 3)); //5
System.Console.WriteLine(c.subtract(1, 3)); //-2
System.Console.WriteLine(c.multiply(13, 2));
System.Console.WriteLine(c.divide(13, 2));
var a = new int[] { 1, 5, 12, -2 };
System.Console.WriteLine(c.add(a)); //16
}