Programming Assignment #2

If you pair-program, put both names in comments at the start of all your code files. Pair programming means all work done together!

This assignment has two problems. One is a console-based C program, similar to what you did in the first assignment. The second, and more interesting in my opinion, is your first program with graphical output. This program will be the seed of a quarter-long project of your design.

Problem #1: Birth Day Calculator

Do Project 60 in Chapter 5 of the textbook. Call the main C file main.c and put it in a folder called PA2.

Problem #2: Your Interactive Graphics Project, part 1

Write a program that draws a simple but non-trivial picture. Call the main C file main.c and put it in a folder called GAME.

What's in the picture is up to you, but it should be something more interesting and complex than just a couple of rectangles or circles. A stack of 3 circles may be a snowman, but it's no challenge.

As the quarter progresses, you're going to make this picture more complex and interactive, like a simple game or a greeting card. So think about what you'd like build along those lines and draw a picture that fits your intended theme.

To compile and run programs with graphics, you need to include not only the code you write, but extra library code. Library code is code other expert programmers have written to do most of the grungy work for you. Your code plus theirs have to be combined together to make a complete working program.

If you use Microsoft's Visual Studio, use these instructions for creating graphics programs.

If you use Bloodshed's Dev-C++, use these instructions for creating graphics programs.

If you are using XCode on a Macintosh, click on this link to download apple-graphlib.zip from the website. It contains the graphics library and instructions on how to set up the library for use with XCode.

How to Tackle The Graphics Problem

Here's my #1 most important rule for programming: take tiny steps.

And #2: think before you code.

Try to start with a working program -- even a trivial program that does nothing. Then add one simple thing, compile and run, debug if necessary. Then add one more simple thing. Compile and run and debug. Never put in more than one new thing without making sure everything still works. If you have to reorganize things, re-organize a little, but don't add anything new. Compile and run. If you do this faithfully, you'll save hours in debugging time.

In the case of your first graphical project, here's my recommended plan of attack.

Think: Plan the drawing

• Before you write any code, get a sheet of graph paper, the kind with large squares, and map out your figure or figures on it. If you don't have any, Google "printable graph paper" for lots of sites that provide graph paper you can print. Remember that you just have a small number of shapes to work with: rectangles, circles, triangles, and lines.
• Draw a rectangle that just surrounds the entire figure. Assign a reasonable size in screen pixels for the width of the rectangle. Set the lower left corner of the rectangle to (0, 0) and calculate where the other corners are for the entire rectangle, and the shapes within it.
• Use these numbers to derive general formulas for the coordinates of every shape. Every shape's coordinates should be of the form (x + a * width, y + b * width), where x and y are the coordinates of the lower left corner (x, y) of the big rectangle, and width is the width of the big rectangle.

By doing this in advance, you'll have a method for drawing your shape that can go anywhere on the screen at any size you want. All you'll need to change are three numbers: x, y and width.

Code: Tiny steps

• Compile and run main.c as it stands. If you don't see the green square, or if clicking on the Quit button doesn't work, stop and post your problem to the newsgroup.
• Replace the code inside the function myDisplay() with code to set x, y, and width, and draw one shape in your figure, with the desired pen color. Compile and run. You should see your shape. Hit any key to quit.
• Now add code to draw the second subshape of your object. Compile and run. Are the two shapes correctly placed and sized? If not, fix.
• Repeat until your shape is complete.
• Create a function. Create a new function to draw your figure, with an appropriate name, e.g., drawDog or drawFlyingSaucer. Move the drawing code in myDisplay() into that function. Define the prototype at the start of the file. For this step, make a function that takes no arguments. Change myDisplay() to call this function. Compile and run.
• Make the function take parameters. Change your drawing function to take parameters of type double for x, y, and width. Delete the lines declaring those local variables in your function. Change myDisplay() to call your function with the appropriate values for x, y, and width. Compile and run.

• Add another call to your drawing function in myDisplay(). This second call should draw your object in another location. Compile and run. Make sure the object appears twice, in the right places, with all the parts properly aligned.