抛出异常

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{

class Program
{
static void Main(string[] args)
{
Console.Write("请输入你要进行的运算及数（+）：");
string f = Console.ReadLine();
Console.Write("请输入第一个数：");
int a = int.Parse(Console.ReadLine());
Console.Write("请输入第二个数：");
int b = int.Parse(Console.ReadLine());
Console.Write("请输入答案：");
int y = int.Parse(Console.ReadLine());
Calldess dss=new Calldess();
try
{
dss.Execute(f, a, b);
throw new DivideByZeroException("尝试除以零吗？");
}
catch (DivideByZeroException e)
{

if (f == "/")
{
if (b == 0)
{
Console.WriteLine(e.Message);
}
}

}

Console.Read();

}
}
public class Calldess
{
int sun;
public int Execute(string op, int a, int b)
{
switch (op)
{
case "+":
sun = a + b;
break;
case "-":
sun = a - b;
break;
case "*":
sun = a * b;
break;
case "/":

if (b == 0)
{
//Console.WriteLine("除数不能为零！");
}
else
{
sun = a / b;
}
break;

}
return sun;

}
}
}