#define ATCI_char_a 'a'
#define ATCI_char_z 'z'

#define ATCI_IS_LOWER( alpha_char )  ( ( (alpha_char >= ATCI_char_a) && (alpha_char <= ATCI_char_z) ) ? 1 : 0 )

#include <iostream>

int main() {
    std::cout << "b: "     << ATCI_IS_LOWER('b') << '\n'
              << "B: "     << ATCI_IS_LOWER('B') << '\n'
              << "Crazy: " << ATCI_IS_LOWER(true || -1) << '\n';
}