//sleep function provided by <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
 
int main(){
  
	printf("Sleeping for 5 seconds \n");
	sleep(5);
	printf("Wake up \n");  
}

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
 
int main(){
  
	printf("Sleeping for 5 seconds \n");
	sleep(5);
	printf("Sleep is now over \n");  
}

#include <unistd.h>

unsigned sleep(unsigned seconds);

#include <Windows.h>
 
int main()
{
    Sleep(500);
}