// 可变字符串的拼接和删除
        NSMutableString *str = [[NSMutableString alloc] initWithString:@"天王盖地虎"];
        [str appendString:@",宝塔镇河妖"]; // 无返回值的拼接字符串
        NSString *str2 = [str stringByAppendingString:@"hahaha"]; // 有返回值拼接字符串
        
        // 删除指定的字符
        NSRange range = [str rangeOfString:@"盖"];// 先确定要删除的字符的范围(位置，长度)
        NSRange range2 = [str rangeOfString:@"镇"];
        
        NSLog(@"%ld-%ld",range2.location,range2.length);
        
        [str deleteCharactersInRange:range]; // 调用删除字符方法
        [str deleteCharactersInRange:range2];
        
        NSLog(@"%ld-%ld",range.location,range.length);
        NSLog(@"%ld-%ld",range2.location,range2.length);
        NSLog(@"%@",str);
        NSLog(@"%@",str2);