//给字符串分配容量

    //stringWithCapacity:

    NSMutableString *String;

    String = [NSMutableString stringWithCapacity:40];

    //在已有字符串后面添加字符  

    //appendString: and appendFormat:

    NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];

    //[String1 appendString:@", I will be adding some character"];

    [String1 appendFormat:[NSString stringWithFormat:@", I will be adding some character"]];

    NSLog(@"String1:%@",String1);

    //在已有字符串中按照所给出范围和长度删除字符

     //deleteCharactersInRange:

     NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];

     [String1 deleteCharactersInRange:NSMakeRange(0, 5)];

     NSLog(@"String1:%@",String1);

     //在已有字符串后面在所指定的位置中插入给出的字符串

    //-insertString: atIndex:

    NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];

    [String1 insertString:@"Hi! " atIndex:0];

    NSLog(@"String1:%@",String1);

    //将已有的空符串换成其它的字符串

    //-setString:

    NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];

    [String1 setString:@"Hello Word!"];

    NSLog(@"String1:%@",String1);

  //outputString1:Hello Word!

    //按照所给出的范围，和字符串替换的原有的字符

    //-setString:

    NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];

    [String1 replaceCharactersInRange:NSMakeRange(0, 4) withString:@"That"];

    NSLog(@"String1:%@",String1);

    //判断字符串内是否还包含别的字符串(前缀，后缀)

    //01：检查字符串是否以另一个字符串开头- (BOOL) hasPrefix: (NSString *) aString;

    NSString *String1 = @"NSStringInformation.txt";

    [String1 hasPrefix:@"NSString"] = = 1 ?  NSLog(@"YES") : NSLog(@"NO");

    [String1 hasSuffix:@".txt"] = = 1 ?  NSLog(@"YES") : NSLog(@"NO");

    //02：查找字符串某处是否包含其它字符串 - (NSRange) rangeOfString: (NSString *) aString，这一点前面在串中搜索子串用到过;