example for ctype.h

#include <stdio.h>
#include <ctype.h>

int main() {
char ch = 'A';

if (isalpha(ch)) {
printf("%c is a letter.\n", ch);

if (islower(ch)) {
  printf("%c is lowercase.\n", ch);
} else {
  printf("%c is uppercase.\n", ch);
}

} else {
printf("%c is not a letter.\n", ch);
}

return 0;
}