Solo MP

This MP, as well as all other MPs in CS 225, are to be completed without a partner.

You are welcome to get help on the MP from course staff, via open lab hours, or Piazza!

Ready, Set

Before starting this MP, make sure you have finished lab_intro.

Lets Go!

This MP is the only one-week MP in CS 225 and is designed to get you set up for future MPs.

Part 1: Getting the files

As with all assignemnts in CS 225, you can download the files by running the following command in your cs225 svn directory:

svn up

If something goes wrong, our SVN Reference has common problems and fixes for you!


If you do not have an account on the svn server, you can still work on this MP by downloading the source files from

Part 2: Create a Makefile

In CS 225, we feel it’s important you understand how a C++ program compiles.

Go through the Makefile Tutorial and create a Makefile for this assignemnt. You may find the lab_intro Makefile useful as a reference.

Your Makefile must compile together your own solution files, namely main.cpp, mp1.cpp, mp1.h, and files in the cs225 directory. Do not have typos in your file names or your Makefile! For example, make sure your Makefile compiles a file named main.cpp, not a file named main.C or test.cpp or any other such thing.

Please make sure your Makefile does not compile extra files that are not part of this MP. For example, do not add in files from the Makefile tutorial by mistake; the only files the Makefile should be dealing with are the few listed in the paragraph above.

Your Makefile must produce an executable called mp1 (all lowercase).

Hint: Makefile for testing

After creating a Makefile that builds mp1, the following two lines can be added to the end of your Makefile so that you can also build the test cases:

test : unit_tests.o mp1.o PNG.o HSLAPixel.o lodepng.o
	$(LD) unit_tests.o mp1.o PNG.o HSLAPixel.o lodepng.o $(LDFLAGS) -o test

unit_tests.o : tests/unit_tests.cpp tests/catch.hpp cs225/PNG.h cs225/HSLAPixel.h
	$(CXX) $(CXXFLAGS) tests/unit_tests.cpp

Part 3: Rotate an Image

Open mp1.cpp and complete the rotate function. This function must:

Here’s alma.png rotated 180 degrees:



In order to complete this, you will need to make use of the CS 225’s PNG class (make sure to add #includes as needed). The CS 225 PNG class is documented here.

Hint: How Do I Rotate an Image?

Take a piece of paper and draw a 5x5 grid on it. Mark the box at (0, 1). Rotate that paper 180 degrees and note where the marked box is now located. Repeat for other squares if necessary.

Can you find the pattern/formula for how the pixel moves?


The Makefile you created must produce an mp1 executable (all lower case mp1). The following command must make mp1:


A main has been provided for you that will call your rotate to read in in.png and output out.png. With that, you may use the given files in_01.png, out_01.png, in_02.png, out_02.png, in_03.png, and out_03.png to test your program. First, copy in_01.png to in.png by typing

cp in_01.png in.png

at the command line. Once your program has run, type

diff out.png out_01.png

to compare your program’s output to out_01.png, which is the output file produced by the solution program written by the course staff.

You are encouraged to test your program on additional images of your own, looking at each output image to see whether it is a perfect 180 degree rotation of the corresponding input image.

Autograder Testing

You can run a subset of the test cases that will be used in the autograder with the following commands:

make test

Grading and Submission

We have provided your output format in the MP specification above, and you need to match that exactly. Testing will be done by comparing your output PNG image file to our own (using the diff utility described in the previous section). If your image file does not match ours, that is considered incorrect output; you do not get partial credit for getting “close”.

When you’re ready to commit a solution, make sure to add all of the files you created:

svn add Makefile
svn add cs225/HSLAPixel.cpp
svn add cs225/HSLAPixel.h

To commit your changes to the repository type:

svn ci -m "mp1 submission"