Lab 8 - Quicksort

Due: 5:00pm on Wednesday

The purpose of this lab is to investigate the quicksort algorithm. This lab will also refresh one's skills at opening files and reading data from files. Additionally, this lab serves as an introduction to the make utility for those that have not taken CMPS 215.

Most of the code for this lab is provided for you in the lab8 directory. Use the following command to create a lab8 subdirectory off your current directory: 

cp -r /home/fac/melissa/public_html/cs223-s10/lab8/ .
The -r option to cp is the recursive option. It will create the lab8 subdirectory and copy all the files over to it.

File Descriptions

file_gen.cpp - This is a variation on the file generator used for Homework 6. It generates data in the range of 0 to 999. It also seeds random with the current time instead of a static value. You compile file_gen.cpp with make file_gen which will make an executable called file_gen
vt100ansi.h - This header file allows colors to be printed to the screen using the macro vtprintf(COLOR) where COLOR is one of the colors defined in the file.
quicksort.cpp - This defines the quicksort algorithm using median-of-three pivots. This version of quicksort puts the pivot in the first slot, instead of the last slot as discussed in class. Both approaches are valid. The code will call insertion sort when the number of elements is less than the defined THRESHOLD value. You can run quicksort in debug mode by defining DEBUG_MODE at the top of the file. In debug mode, information about choosing the pivot, making the swaps and doing insertion sort are printed to the screen. Since there is a lot of information, SLEEP_USEC defines how long the debug mode pauses between stages so that the information can be read. You can turn this pausing off by defining SLEEP_USEC as 0 at the top of the file.
lab8main.cpp - This is the main program. You will need to fill in a little code to open the specified file and read the data into the local array. (Note: You will need to do a similar task to this in Homework 6 too). To compile lab8main.cpp after making the required changes, type make main. This will create an executable called main, which can be run with main input1 or any other filename.
input1, input2 and input3 - Pre-generated input files containing 40 integers each.
Makefile - A makefile to compile the above code into executables. This is needed for the make commands to work.

Make utility

The make utility and its associated Makefile is a way to specify program dependencies, particularly when one is using seperate compilation. The Makefile defines all the associations in the form of: 
target:   dependency list
   compilation command
You then tell make to compile certain targets by giving the command make <target>.

Misc. Notes

This works best if you are using a color terminal with scrollback capacity. If you are using your laptop instead of the machines in 311, make sure that your terminal supports VT100 ANSI colors. Putty for Windows should work, as should the Mac OS X terminal. The pausing code may behave oddly if you try to download it and compile it on Windows (even though there is a workaround in the code, Windows does poorly with this sort of task), so make sure to log into Sleipnir and try the code there.

Assignment

Fill in the required portion of lab8main.cpp which involves opening a file for reading and reading in the integers. Once you have added the file I/O code, compile the program with make main. Test different file sizes and see how quicksort partitions the lists. Notice how even when the list is not partitioned in the middle, the split operation still runs quickly.

Turn off debugging mode by removing, commenting out or undefining the DEBUG_MODE line and recompile the program with make main. Try running the following: 

time main input1
This will show you how long it takes to run the quicksort executable for input1. You can try this for all the files you've generated for this lab. However, Sleipnir is pretty fast, so you may not notice much of a time difference with the defined MAX_CAPACITY.

Email me your modified lab8main.cpp.