#include <windows.h>

int main(){
 MessageBox(
  0,
  "Hello world!",
  "Zufolek rules the universe",
  MB_ICONASTERISK | MB_OK
 );
 return 0;
}

For MinGW or Cygwin, compile wth -mwindows option to get rid of console.

Try replacing the MB_OK with MB_OKCANCEL and see what happens.

Simple Windoze Program

C