COMP 2673 - Lab3
                        In-lab Assignment
Goals:
Introduction to ddd - After this lab you should know:
    how to compile a program so that it can be debugged
    how to start and quit ddd
    how to set breakpoints, run, step into, step over, and continue
    how to examine the values of variables
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What is GDB?
GDB, the GNU Project debugger, allows you to see what is going on `inside' 
another program while it executes -- or what another program was doing at the 
moment it crashed.

GDB can do four main kinds of things to help you catch bugs in the act:

1. Start your program, specifying anything that might affect its behavior. 
2. Make your program stop on specified conditions. 
3. Examine what has happened, when your program has stopped. 
4. Change things in your program, so you can experiment with correcting the 
effects of one bug and go on to learn about another.

The program being debugged can be written in C, C++, Pascal (and many other 
languages). Those programs might be executing on the same machine as GDB 
(native) or on another machine (remote). GDB can run on most popular UNIX and 
Microsoft Windows variants.

In this lab, we would use ddd (Data Display Debugger), which is a GUI version
of gdb.
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Steps:

1. Go to your directory IntroToCS3.
2. Copy the file ~sarora/IntroToCS3/linkedlist.tgz  to your directory.
3. Extract the assignment 3 files from this file using the command:
	tar -xvzf linkedlist.tgz
4. The above command will create a directory "linkedlist".
5. Enter this directory.
6. Compile the files by typing "make". This creates an executable file by
   the name "executable". "executable" is a program that performs addition,
   deletion and traversal on linked lists, and it has some bugs that we will
   locate and fix using debugger in today's lab.
7. If you look in the Makefile, the files have been compiled using the "-g"
   option. This option stores debug information in the "executable", which is
   essential if you want to use a degugger on this executable. You would want
   to remove this option once the executable is working correctly as this extra
   information slows down execution of the program.
8. Open the file in the debugger by typing "ddd executable &". This would open 
   the source file (corresponding to the executable) which contains the 
   function "main()". In this case it will open "llist.cpp" in the ddd window
   (because "llist.cpp" is the file corresponding to "executable" that contains
   the function "main()").
9. Click close on the dialog box "DDD Tip of the day".
10. Set a breakpoint on the first line inside the function main() as follows:
    - Right click on the beginning of that line.
    - Select "Set Breakpoint".
11. Start running the program in the debugger by pressing F2 and then in the 
    dialog box which appears click "Run".
12. Press <Alt>8 to view the command tool.
13. Execute the program in the debugger, and experiment with the following
    commands:
    - Click "Step" in the command tool window to "step inside" the statement.
    - Click "Next" in the command tool window to run the next statement.
    - Click "Cont" in the command tool window to continue execution till the
      the next "termination point", which is either a Breakpoint you have set,
      a fatal error in the program or the end of program.
    - Toggle a breakpoint by moving the cursor to a line and using the "stop" 
      button.
14. The execution stops at the line (green arrow becomes a broken red arrow):
	cout<<temp->Data<<" -> ";
15. Press <Alt>3 to view the data window.
16. In the data window, right click and select "New Display...".
17. In the dialog box for "New Display" type "temp" and click "Display".
18. The value of variable "temp" shows up in the data window.
19. Right click on this value and select "Display *()".
20. The value of location pointed to by "temp" shows up in the data window.
21. Start running the program again by clicking "Run" in the command tool.
22. In the dialog box which appears click "Yes".
23. Click "Next" in the command tool window.
24. Click "Step" in the command tool window.
25. The variable "temp" becomes visible in the data window.
24. Click "Next" again in the command tool window.
25. The change in the value of the variable "temp" can be seen in the data
    window.
26. Click "Next" repeatedly in the command tool window until the program
    crashes (the green arrow becomes a broken red arrow) .
27. Write down on a piece of paper your name and the reason you think the
    program crashed. Also suggest a way (i.e. give correct code for that part)
    to fix this bug. Turn-in this paper to TA.
28. (EXTRA CREDIT) Figure out (on your own) how to set a "temporary breakpoint",
    experiment with "temporary breakpoint" and figure out the difference between
    a "breakpoint" and a "temporary breakpoint". Write down the difference on
    on a piece of paper and Turn-in this paper to TA.
29. Quit the debugger by pressing <Ctrl>Q.