What is the proper #include for the function 'sleep()'?

this is what I use for a cross-platform code:

#ifdef _WIN32
#include <Windows.h>
#else
#include <unistd.h>
#endif

int main()
{
  pollingDelay = 100
  //do stuff

  //sleep:
  #ifdef _WIN32
  Sleep(pollingDelay);
  #else
  usleep(pollingDelay*1000);  /* sleep for 100 milliSeconds */
  #endif

  //do stuff again
  return 0;
}

The sleep man page says it is declared in <unistd.h>.

Synopsis:

#include <unistd.h>

unsigned int sleep(unsigned int seconds);

sleep is a non-standard function.

• On UNIX, you shall include <unistd.h>.
• On MS-Windows, Sleep is rather from <windows.h>.

In every case, check the documentation.