C#输入的类型转换

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

namespace ConsoleIO
{
    class Program
    {
        static void Main(string[] args)
        {
             Console.Write("Please enter the first number: ");
             string strFirst = Console.ReadLine();

             Console.Write("\nPlease enter the second number: ");
             String strSecond = Console.ReadLine();

             //Int32.Parse(strFirst)
             int iFirst = Convert.ToInt32(strFirst);
             //Int32.Parse(strSecond)
             int iSecond = Convert.ToInt32(strSecond);
             int iResult = iFirst - iSecond;

             Console.WriteLine("the result is : " + iResult);

             Console.ReadLine();
        }
    }
}