C#中的if语句

if语句的使用方法：

using System;

namespace IfDemo
{
class Program
{
static void Main()
{
Console.WriteLine("Please input a string:");
string input = Console.ReadLine();

if(input == "")
{
Console.WriteLine("You typed in an empty string!");
return ;
} else if(input.Length < 10)   //这里的 else if 可以根据需要添加多个
{
Console.WriteLine("The string had less than 10 characters.");
} else if(input.Length < 10)
{
Console.WriteLine("The string had at least 10 but less than 20 characters.");
}else {            //这里的else 只能有一个
Console.WriteLine("The string had more than 20 characters.");
}

Console.WriteLine("The string was {0}",input);

Console.ReadKey();
}
}
}