NSMutableString *mutableStr = [[NSMutableString alloc] initWithFormat:@"蓝鸥科技有限公司"];

NSMutableString *mutableStr1 = [NSMutableString stringWithFormat:@"蓝鸥科技有限公司"];

//拼接字符串

         [mutableStr appendString:@".txt"];

         NSLog(@"%@", mutableStr);

//插入

         [mutableStr1 insertString:@"3G" atIndex:2];

         NSLog(@"%@", mutableStr1);

//删除

       [mutableStr1 deleteCharactersInRange:NSMakeRange(2, 2)];

         NSLog(@"%@", mutableStr1);