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();        }    }}