/****** w3.C ******/
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/Xos.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
{
 Display *disp;
 int ScrNum;
 GC prGC;
 XEvent Evnt;
 Window win;
 char str[100]="Hello world!";
 
 if ( (disp = XOpenDisplay (NULL)) == NULL)
  {
    printf("\n====1");
    exit(1);
  }
 
 ScrNum = DefaultScreen( disp );
 
 win = XCreateSimpleWindow( disp, RootWindow( disp, ScrNum), 0, 0, 100, 100, 2, 
                                  BlackPixel(  disp, ScrNum), WhitePixel(  disp, ScrNum) );

 XSelectInput( disp, win, ExposureMask|KeyPressMask );

 XMapWindow (disp,win);

 while( 1 )
  {
    XNextEvent( disp, &Evnt);
    switch (Evnt.type)
     {
      case Expose:
        if ( Evnt.xexpose.count!=0 ) break;
         prGC = XCreateGC( disp, win, 0, NULL );
         XSetForeground( disp, prGC, BlackPixel(disp, 0) );
         XDrawString( disp, win, prGC, 10,50, str, strlen(str) );
         XFreeGC( disp, prGC );
       break;
      case KeyPress:
       goto fin; 
     }
  } 
fin:
 XCloseDisplay( disp ); 
 return 0;
}