HW3ex2

#include <stdio.h>

#define OS 1

int main() {
    #ifndef OS
        fprintf(stderr, "OS is undefined!\n");
        return 2;
    #endif

    #if(OS == 1)
        printf("Linux\n");
    #elif(OS == 2)
        printf("Windows\n");
    #elif(OS == 3)
        printf("macOS\n");
    #endif

    return 0;
}