C#运用try-catch-finally语句处理异常

在输入两个数字进行相加的操作时，若输入的内容不符合要求会出现异常，在C#程序中可用try-catch-finally语句处理异常，具体代码为：

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

namespace trysample_10._12_
{
    class Program
    {
        static void Main(string[] args)
        {
            calculator c = new calculator();
            int r = c.add("120", "240");
            Console.WriteLine(r);
        }
    }
    class calculator
    {
        public int add(string str1,string str2)
        {
            int x = 0;
            int y = 0;
            bool haserror = false;
            try
            {
                x = int.Parse(str1);
                y = int.Parse(str2);
            }
            catch(ArgumentNullException ane)
            {
                Console.WriteLine(ane.Message);
                haserror = true;
            }
            catch(FormatException fe)
            {
                Console.WriteLine(fe.Message);
                haserror = true;
            }
            catch(OverflowException oe)
            {
                Console.WriteLine(oe.Message);
                haserror = true;
            }
            finally
            {
                if(haserror==true)
                {
                    Console.WriteLine("The program has error!");
                }
                else
                {
                    Console.WriteLine("Right!");
                }
            }
            int result = x + y;
            return result;
        }
    }
}

若输入内容正确，结果为：

若输入内容不正确，程序会在命令行窗口报错并显示具体错误原因，结果为：