When i compile acode i have this error cannot open file X11/Xlib.h in c++
<pre><code>/* Sequential Mandelbrot program mandelbrot.c */

#include &lt;X11/Xlib.h&gt;
#include &lt;X11/Xutil.h&gt;
#include &lt;X11/Xos.h&gt;
#include &lt;stdio.h&gt;
#include &lt;string.h&gt;
#include &lt;math.h&gt;

#define           X_RESN      800       /* x resolution */
#define           Y_RESN      800       /* y resolution */

typedef struct complextype
{ float real, imag;
} Compl;

int main (int argc, char *argv[])
{  Window     win;                 /* window initialization */
   unsigned 
   int        width, height,       /* window size */
              x, y,                /* window position */
              border_width,        /* border width in pixels */
              display_width, 
              display_height,      /* size of screen */
              screen;              /* which screen */

   char      *window_name = "Mandelbrot Set", *display_name = NULL;
   GC         gc;
   unsigned   long valuemask = 0;
   XGCValues  values;
   Display   *display;
   XSizeHints size_hints;
   Pixmap     bitmap;
   XPoint     points[800];
   FILE          *fp, *fopen ();
   char           str[100];

   XSetWindowAttributes attr[1];

/* Mandlebrot variables */
   int i, j, k;
   Compl    z, c;
   float    lengthsq, temp;

/* connect to Xserver */

   if (  (display = XOpenDisplay (display_name)) == NULL ) 
   {  fprintf (stderr, "drawon: cannot connect to X server %s\n",
                        XDisplayName (display_name) );
      exit (-1);
   }

/* get screen size */

   screen = DefaultScreen (display);
   display_width = DisplayWidth (display, screen);
   display_height = DisplayHeight (display, screen);

/* set window size */

   width = X_RESN;
   height = Y_RESN;

/* set window position */
   x = 0;
   y = 0;

/* create opaque window */

   border_width = 4;
   win = XCreateSimpleWindow(display, RootWindow (display, screen),
        x, y, width, height, border_width, 
        BlackPixel (display, screen), WhitePixel (display, screen));

   size_hints.flags = USPosition|USSize;
   size_hints.x = x;
   size_hints.y = y;
   size_hints.width = width;
   size_hints.height = height;
   size_hints.min_width = 300;
   size_hints.min_height = 300;

   XSetNormalHints (display, win, &amp;size_hints);
   XStoreName(display, win, window_name);

/* create graphics context */

   gc = XCreateGC (display, win, valuemask, &amp;values);
   XSetBackground (display, gc, WhitePixel (display, screen));
   XSetForeground (display, gc, BlackPixel (display, screen));
   XSetLineAttributes (display,gc,1,LineSolid,CapRound,JoinRound);
   attr[0].backing_store = Always;
   attr[0].backing_planes = 1;
   attr[0].backing_pixel = BlackPixel(display, screen);

   XChangeWindowAttributes(display, win, 
        CWBackingStore | CWBackingPlanes | CWBackingPixel, attr);
   XMapWindow (display, win);
   XSync(display, 0);

/* Calculate and draw points */

   for(i=0; i &lt; X_RESN; i++) 
   {  for(j=0; j &lt; Y_RESN; j++) 
      {  z.real = z.imag = 0.0; /* 800x800 scale factors */
         c.real = ((float) j - 400.0)/200.0;  
         c.imag = ((float) i - 400.0)/200.0;
         k = 0;

         do
         {                      /* iterate for pixel color */
             temp = z.real*z.real - z.imag*z.imag + c.real;
             z.imag = 2.0*z.real*z.imag + c.imag;
             z.real = temp;
             lengthsq = z.real*z.real+z.imag*z.imag;
             k++;

         } while (lengthsq &lt; 4.0 &amp;&amp; k &lt; 100);

         if (k == 100) XDrawPoint (display, win, gc, j, i);
   }  }

   XFlush (display);
   sleep (30);

/* Program Finished */
}
</code></pre>
