/*** Operating system detection ***/
#include<stdio.h>

#if defined(linux) || defined(_linux) || defined(__linux__) || defined(__unix__)
  #define OSTYPE 1
#elif defined(_WIN32) || defined(_WINDOWS) || defined(__WINDOWS__)
  #define OSTYPE 2
#elif defined(MSDOS) || defined(_MSDOS) || defined(__MSDOS__)
  #define OSTYPE 3
#elif (defined(__MACH__) && defined(__APPLE__))
  #define OSTYPE 4
#else
  #define OSTYPE 0
#endif

int main(){
   switch(OSTYPE){
     case 1:
       printf("This is a Unix/Linux system.\n");
       break;
     case 2:
       printf("This is a Windows system.\n");
       break;
     case 3:
       printf("This is a MS-DOS system.\n");
       break;
     case 4:
       printf("This is an Apple/Machintos system.\n");
       break;
     default:
       printf("I don't know what kind of operating system is this.\n");
     }
   return 0;
   }