Objective-C NSString

// 创建字符串
    NSString *str = @"hi, jzh蒋";
    // 字符串长度，OC中英文都占1个字节
    NSLog(@"%ld", [str length]);
    // 格式化字符串
    NSString *str1 = [NSString stringWithFormat:@"格式化 %02d- %02d", 1, 9];
    NSLog(@"%@", str1);
    // 字符串拼接
    NSString *str2 = [NSString stringWithFormat:@"%@%@", str, str1];
    NSLog(@"%@", str2);