The example shown at https://mattiasgustavsson.itch.io/dos-like doesn’t compile anymore, a few minor changes are needed.

Something like this:

#include <stdlib.h>
#include "dos.h"

int main(int argc, char* argv[])
{
  setvideomode(videomode_320x200);

  while(!shuttingdown())
  {
    waitvbl();

    for(int i = 0; i < 5; ++i)
    {
      setcolor(rand() % 256);
      line(rand() % 320, rand() % 200, rand() % 320, rand() % 200);
      setcolor(rand() % 256);
      fillcircle(rand() % 320, rand() % 200, rand() % 30);
      setcolor(rand() % 256);
      circle(rand() % 320, rand() % 200, rand() % 30);
    }

    if(keystate(KEY_ESCAPE)) break;
  }

  return 0;
}

Ah, yes, I changed the API to be more aligned with the old Borland BGI from the DOS days, but forgot to update that code. I've updated it now, thanks for reminding me :)