char c = 'a';
// ctype.h functions take an unsigned char value
// and return any nonzero int for yes; bool turns it into 1.
bool isUpper = isupper((unsigned char)c);
bool isLower = islower((unsigned char)c);
//isUpper is false
//isLower is true
printf("isUpper is %s\n", isUpper ? "true" : "false");
printf("isLower is %s\n", isLower ? "true" : "false");