C# string

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using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace String{    class Program    {        static void Main(string[] args)        {            //字符串相当于字符数组            string sentence = "hello";            char letter = sentence[0];            Console.WriteLine(letter);//输出h            char[] letter1 = { 'h', 'e', 'l', 'l', 'o' };            string sentence1 = new string(letter1);            Console.WriteLine(sentence1);//输出 hello            string sentence2 = new string('a', 10);            Console.WriteLine(sentence2);//输出 aaaaaaaaaa            //复制字符串            string sentence3 = "hello";            string sentence4 = sentence3;            Console.WriteLine(sentence4);//输出hello,s4指向s3的内存地址            sentence3 = "hi";            Console.WriteLine("{0},{1}", sentence3, sentence4);//输出hi,hello，字符串的内容不能改变，一旦改变系统就会申请新的内存空间，所以s4指向原来的s3内存地址，s3现在的内存地址是系统新分配的            string sentence5 = string.Copy(sentence4);            Console.WriteLine("{0},{1}", sentence4, sentence5);//输出hello,hello,不过Copy函数，会重新给s5分配新的内存空间，内容是s4字符串的内容            char []str = { '1', '2', '3', '4', '5' };            sentence5.CopyTo(0,str,0,5);//把sentence5的内容复制到str中，第一个参数表示从sentences的莫个参数开始，第二参数指字符数组对象，第三参数表示字符数组开头的编号，第四个参数表示总共复制的字符的个数            Console.WriteLine(str);//输出hello            //比较字符串            string string1 = "hello";            string string2 = "hello";            if (string1 == string2)                Console.WriteLine("相等");//输出相等            else                Console.WriteLine("不相等");            if (string2.Equals("hello"))                Console.WriteLine("相等");//输出相等            else                Console.WriteLine("不相等");            if(string.Equals(string1,string2))                Console.WriteLine("相等");//输出相等            else                Console.WriteLine("不相等");            switch(string1.CompareTo(string2))            {                case -1: Console.WriteLine(string1 + "<" + string2); break;                case 0: Console.WriteLine(string1 + "==" + string2); break;//输出hello==hello                case 1: Console.WriteLine(string1 + ">" + string2); break;            }        }    }}
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