#include <stdio.h>
#include <unistd.h>

int main(void)
{
        if (isatty(0)) {
                fprintf(stderr, "stdin is a tty\n");
        } else {
                fprintf(stderr, "stdin is not a tty\n");
        }

        if (isatty(1)) {
                fprintf(stderr, "stdout is a tty\n");
        } else {
                fprintf(stderr, "stdout is not a tty\n");
        }
        return 0;
}