C computer setup

High School C programming examples by Halverson. How to set things up.

The c and c++ programming examples I have posted here are being run on old PCs that have Ubuntu Version 8 Linux installed. The latest Ubuntu is Version 12, and now version 8 is no longer supported.

If you are like me, running Ubuntu 8, then the first thing to do is to tell the computer that we must get the obsolete C libraries and support code, because getting the latest code would just mess things up. I got this information from here:
http://askubuntu.com/questions/48025/what-to-do-when-cant-update-anymore-with-apt-get

Here is what you do if you are using obsolete Ubuntu 8 (You can skip down if you use Ubuntu 12 or later):

--- Log in to a full privileged account (whoever set up the computer)

--- Edit the file that controls where on the web software is to be downloaded. But first we’ll do a backup.
--- Start the terminal

cd /etc/apt
sudo cp sources.list sources.backup
sudo gedit sources.list

---In the editor, do a control-H (Find and Replace) and replace all instances of "us.archive" with "old-releases"
--- Save and exit the editor
--- (The next command will give you some security errors, but it will still work.)

------------- Skip to here if using Ubuntu 12. Either way, you must do the next three steps. -------------

sudo apt-get update
sudo apt-get install build-essential
sudo apt-get install libx11-dev

--- Try this X-Windows test program. First go your “home”, then start the editor.

cd ~
gedit xwindowtest.c &


// ============== xwindowtest.c ======================

// This is the command to compile it.  Note that it uses C++ because the x-window graphics library
// was written in C++

// g++ xwindowtest.c -o xwindowtest -lX11

// After you compile it, this is the command to run it:   ("./" means to run the program that is "here")

// ./xwindowtest

// Written by Ch. Tronche (http://tronche.lri.fr:8000/)
// Copyright by the author. This is unmaintained, no-warranty free software. 
// Please use freely. It is appreciated (but by no means mandatory) to
// acknowledge the author's contribution. Thank you.
// Started on Thu Jun 26 23:29:03 1997

//
// Xlib tutorial: 2nd program
// Make a window appear on the screen and draw a line inside.
// If you don't understand this program, go to
// http://tronche.lri.fr:8000/gui/x/xlib-tutorial/2nd-program-anatomy.html
//
// Compile command:
// g++ -Wall -W -Werror xwindowtest.c -o xwindowtest -lX11

#include <X11/Xlib.h> // Every Xlib program must include this
#include <assert.h>   // I include this to test return values the lazy way
#include <unistd.h>   // So we got the profile for 10 seconds

#define NIL (0)       // A name for the void pointer

int main()
{
      // Open the display

      Display *dpy = XOpenDisplay(NIL);
      assert(dpy);

      // Get some colors

      int blackColor = BlackPixel(dpy, DefaultScreen(dpy));
      int whiteColor = WhitePixel(dpy, DefaultScreen(dpy));

      // Create the window

      Window w = XCreateSimpleWindow(dpy, DefaultRootWindow(dpy), 0, 0, 
                                 200, 100, 0, blackColor, blackColor);

      // We want to get MapNotify events

      XSelectInput(dpy, w, StructureNotifyMask);

      // "Map" the window (that is, make it appear on the screen)

      XMapWindow(dpy, w);

      // Create a "Graphics Context"

      GC gc = XCreateGC(dpy, w, 0, NIL);

      // Tell the GC we draw using the white color

      XSetForeground(dpy, gc, whiteColor);

      // Wait for the MapNotify event

      for(;;) {
      XEvent e;
         XNextEvent(dpy, &e);
      if (e.type == MapNotify)
                break;
      }

      // Draw the line
      
      XDrawLine(dpy, w, gc, 10, 60, 180, 20);

      // Send the "DrawLine" request to the server

      XFlush(dpy);

      // Wait for 10 seconds

      sleep(10);
      return(0);
}

Peter G. Halverson, Ph.D.