char&String&StringBuilder

Char.IsLetter(a)

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String.Compare("aaa","bb");

b>a
大于返回1 相等返回0 小与返回-1 

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String.Equals("a","b");
true false

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str2.Insert(0,"a");

插入字符串

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"wertyui"
str2.Remove(3);

"wer"

数组
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"qwerty"
str2.Remove(1,2);

"qrty"

数组
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strb=String.Copy(stra);

复制a给b

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str1.CopyTo(1,"abcdef",0,4);

"yy"

"bcde"


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a.Replace("a","b");

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StringBuilder MY=new StringBuilder("HELLOWORLD");
省位置。需要不断修改。
一个MY用多次


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