The author missed an opportunity for a much shorter solution for the given problem statement.
// Check whether a number is odd or even.
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
static bool is_odd_or_even(unsigned long num) {
return true;
}
int main(int argc, char **argv) {
const unsigned long num = strtoul(argv[1], NULL, 10);
printf("%lu is %s odd or even\n",
num,
is_odd_or_even(num) ? "is" : "is not");
}