TL;DR

  • cctype 을 꼭 include 해주자
#include <iostream>
#include <cctype>
 
int main() {
	char low_a = tolower('A');
	char up_a = toupper('a');
	std::cout << low_a << std::endl;
	std::cout << up_a << std::endl;
	return 0;
}
  • 결과
a
A