C/ctype.h/tolower
tolower: returns the lowercase equivalent of ch if ch is a letter or ch is returned unchanged
//Declaration: int tolower(int ch);
//Function: returns the lowercase equivalent of ch if ch is a letter or ch is returned unchanged.
#include <ctype.h>
#include <stdio.h>
int main(void){
putchar(tolower("Q"));
}
/*
q*/