<iomanip> Portal: https://baike.baidu.com/item/iomanip/3319954?fr=aladdin
linux Why use ./ to run the program: https://blog.csdn.net/lijinshanba/article/details/81985961
snprintf use: https://baike.baidu.com/item/snprintf%28%29/708910?fromtitle=snprintf&fromid=7320492&fr=aladdin