题目如下:
代码:
```c#
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Day06
{
class Program
{
static void Main(string[] args)
{
string str = "How are you";
//1
string[] str1 = str.Split(' ');
for (int i = str1.Length - 1; i >= 0; i--)
{
Console.Write(str1[i]);
Console.Write(" ");
}
Console.WriteLine();
//2
for (int i = str1.Length - 1; i >= 0; i--)
{
for (int j = str1[i].Length - 1; j >= 0; j--)
Console.Write(str1[i][j]);
Console.Write(" ");
}
//3
Console.WriteLine();
str = str.Trim();
for (int i = 0;i<str.Length ;i++ ) {
int a = str.IndexOf(str[i]);
int b = str.LastIndexOf(str[i]);
if (a == b)
Console.Write(str[i]+" ");
}
}
}
}
## 运行结果:

## 注意事项:
1.==Split方法返回的数组可以理解为交错数组(一维数组里面包含着一维数组)。==
2.这三道题考察的是对string相关方法的理解和运用,以下列出几个常用的string方法
## ToArray Insert Contains Tolower ToUpper IndexOf Substring Trim Replace Join