main(){
...
return 0;
}
https://www.csie.ntu.edu.tw/~b98902112/cpp_and_algo/cpp02/character.html
https://www.csie.ntu.edu.tw/~b98902112/cpp_and_algo/index.html
https://yuihuang.com/apcs
https://www.w3schools.com/cpp/default.asp