CMSC 106 Project #3 - Gemstones Spring 2003


Due date: Wednesday, March 19 before 11:00 p.m.

1 Purpose

In this project you will write a program using loops and nested loops. Although as a matter of style and clarity it is usually extremely important to use the most appropriate type of loop for each iterative task in a program, in order to get practice with all of C's loop statements, we suggest that you intentionally use some of each type in your project.

You are developing a game program which uses gemstones of various shapes. Unfortunately, your order for a graphics terminal has been delayed, because all available graphics chips are being used to construct slot machines. So, you decide to draw your shapes using patterns of asterisks.

Your program will use asterisks to draw any size versions of triangles, diamonds, parallelograms, and trapezoids. It will also draw the shapes with rotations in multiples of 90 degrees. Here are some non-rotated shapes with base width 11:

Triangle
     *
    ***
   *****
  *******
 *********
***********

Diamond
     *
    ***
   *****
  *******
 *********
***********
 *********
  *******
   *****
    ***
     *

Parallelogram
       ***********
      ***********
     ***********
    ***********
   ***********
  ***********
 ***********
***********

Trapezoid
   *****
  *******
 *********
***********

There are some restrictions on the dimensions of the various shapes. These will be descrbed below. It is important that you use the exact style given for each shape in your output.

2 Project description

The input to your program is to consist of a sequence of input lines (redirected from an ASCII text file using standard UNIX input redirection). Each line will contain 4 integers. These will be:

  1. shape code - The possible shape codes are:

    1. 1 for triangle
    2. 2 for diamond
    3. 3 for parallelogram
    4. 4 for trapezoid

  2. base size for the shape

  3. height for the shape

  4. rotation in number of degrees (clockwise) to rotate the shape before drawing it

There are some restrictions on the values which may be used. They are listed under "Error Checking" below.

As an example, suppose the program receives the following line of input:

3 11 8 0

This instruction says: ``Draw shape code 3 (parallelogram), sized so that it is 11 wide by 8 high, and rotate the shape 0 degrees before drawing it. (This is the command which could be used to draw the parallelogram shown above.)

The last line in the input will always contain a shape code of -1; it may or may not contain other data items. This is the signal that the program should terminate. (Do not try to draw anything or print any error messages when this line is processed.)

2.1 Error Checking

For this project you must do some error checking of the input values. You may assume (without checking) that each line will contain the proper number of integer values. However, you must check that these values are within the ranges specified below.

VALID RANGES:

shape code: 1 through 4 (inclusive)

size:

rotation: any multiple of 90

IMPORTANT: You will output AT MOST one error message for each line processed (even if more than one of the values is out of range.) In other words, there will be exactly one error message for each line that contains an error. Below are instructions on how to prioritize your error messages.

First check if the shape code is out of range. If it is out of range, you will print the error message below and move on to the next line in the input. (DO NOT PRINT MORE THAN ONE ERROR MESSAGE, EVEN IF THE SIZE AND ROTATION VALUES ARE ALSO OUT OF RANGE.)

ERROR: ILLEGAL SHAPE CODE

Assuming that the shape code is in the correct range, you will next check the base size entered. If the base size entered is not valid, you must print the message below, and move on to the next line in the input. (DO NOT PRINT MORE THAN ONE ERROR MESSAGE, EVEN IF THE HEIGHT AND ROTATION VALUES ARE ALSO OUT OF RANGE.)

ERROR: ILLEGAL BASE

Assuming that the base size is in the correct range, you will next check the height entered. If the height entered is not valid, you must print the message below, and move on to the next line in the input. (DO NOT PRINT MORE THAN ONE ERROR MESSAGE, EVEN IF THE ROTATION VALUE IS ALSO OUT OF RANGE.)

ERROR: ILLEGAL HEIGHT

Assuming that the shape code and size values are all in the correct range, you must still check that the rotation value is acceptable. If it is not a valid rotation amount, you must print the message below, and move on to the next line of input.

ERROR: ILLEGAL ROTATION AMOUNT

2.2 Drawing Shapes

Here are some specific instructions on drawing the shapes:

3 Primary Input

As usual, we are providing you with a primary test case to get you started. Remember that we will be testing your projects with many other sets of data, so it is important that you test your project thoroughly with all sorts of data before submitting it.

Below is the primary input file that we are providing:

1 9 5 90
3 4 7 0
2 5 5 0
1 1 1 0
4 5 2 0
-1 -1 -1 -1

4 Sample Output

Below is the output your program should produce if it is given the input shown above. Note that your output must look EXACTLY as below. (Please observe that there is always one blank line after each shape drawn.) IMPORTANT: Some of you have been submitting projects where the output is close but not quite correct, even for the primary case. It is your responsibility to check your output using ``diff''. If your output for the primary case is not IDENTICAL to ours for any reason, then you will be penalized.

*
**
***
****
*****
****
***
**
*

      ****
     ****
    ****
   ****
  ****
 ****
****

  *
 ***
*****
 ***
  *

ERROR: ILLEGAL BASE

 ***
*****

5 Project requirements

All your C programs in this course should be written in ANSI C, which means they must compile and run correctly with cc -std1 -trapuv on the OIT UNIX Class Cluster. You will lose credit if your program generates any warning messages when it is compiled. Even if you already know what they are, you may not use any C language features other than those introduced in Chapters 1 through 6 of your textbook, plus those presented in lecture while these chapters were covered. Note that as a result character variables, arrays and user-defined functions may not be used. In addition, neither the goto nor the continue statement may be used, and the break statement may not be used in any loop. Lastly, your program must contain only one single return statement at its end, and may not use the exit() function at all. Using C features not in these chapters, or using the goto statement, multiple returns, or break or continue in loops will result in losing credit.

Your program must have a comment near the top which contains your name, login ID, student ID, your section number, your TA's name, and an original description of the action and operation of the program. Your program should be written using good programming style and formatting, as discussed in class and throughout your textbook. For this project, style is considered to consist of:


6 Deadline

Your project must be electronically submitted by the deadline stated above to avoid losing credit per 24 hours as indicated on the syllabus. No project more than 48 hours late will be accepted without prior permission or a valid medical excuse, as described on your syllabus. Lost passwords or other system problems do not constitute valid justifications for late projects. You should start working on your project now!

7 Developing your program

You may want to skip this section at first, read the rest of the project, and come back to study it carefully when you are about to begin writing your program.

One of the important skills which must be learned in this course is how to track down the causes of and fix both syntax and semantic errors in your code. As your program will inevitably have many errors while you are developing it, you will need to follow procedures such as those described below before coming to office hours for assistance. Should you still not be able to solve the problem and have to come to office hours, you will be required to clearly describe your error and what you have already done to try and find it, and bring current printouts of your source code, and any compiler errors or execution results.

7.1 Possible development steps

As mentioned in the earlier project assignments it is extremely important to type in only a part of your program at a time and compile and test it to verify that it is correct before going on. Different choices can be made in selecting which parts of a program to implement first; the following is just one possibility. It's fine if you prefer to follow different steps, but whichever order you choose to develop your program it is essential to enter small parts at a time and test each one before going on!


  1. The first step in developing a program very often should be to read the required input values and just print them out to verify that they were read correctly. If your program isn't reading its input properly, obviously no subsequent processing can ever be correct. Also make sure the program can stop when it reads the last line containing a shape code of -1.

  2. Next you may want to assume the user will put in valid input for a while. Make sure the input files you create for this stage do not contain any invalid values.

    Be sure to compile and thoroughly test the code implementing this step (in fact, you could implement this step itself in several substeps, testing each as you go). These substeps could include assuming at first that the user will only ask for a triangle. Then a parallelogram, and so on. You may want to assume that the rotations are all 0 until you are able to print all shapes in their usual orientation first. Take each step allowing more flexibility in the input - make sure you have the correct values in your input file for the development level you are assuming at that time.

  3. Then expand your program so that it can determine invalid input and respond correctly.

7.2 Finding compilation errors

  1. If you implement your project in sections as described above, a syntax error which appears will most likely be caused by something in the code which was most recently added. Start by looking at these lines and the lines directly adjacent to them.

  2. Some types of syntax errors (such as missing or mismatched braces) can't be recognized by the compiler until some point in the program after the actual mistake, sometimes not even until the end of the program file. If a syntax error is identified at the end of your program, or if a syntax error is generated for a seemingly correct line, this type of error might be the cause, so examine your braces carefully, making sure they all match up properly

    A useful strategy to use for narrowing down the cause of such types of errors is to comment out one section of the program at a time and recompile it after each part is commented out, until the syntax error goes away. At that point, the cause of the error must be in the most recently commented-out code. If you comment out parts of your code your program certainly won't work correctly, but this technique is just to help you quickly find the syntax error, and once you correct it you can just remove the /* and */ symbols which you added to comment out your code.

    A few things to keep in mind about this technique are as follows. You can't comment out only a part of a larger statement, for instance, you can't comment out the first half of an if statement but leave the else part- you would have to comment out the whole if/else. You can't comment out half of a compound statement such as the opening brace ({) and some of the statements inside but leaving the closing brace (}) uncommented as part of the code- you would have to comment out the whole compound statement. You also can't comment out code containing comments- you would have to copy your program to a different file, delete the comments, and then use this strategy. Once you find the syntax error in this temporary copy of your program you can correct it in your real version.

7.3 Creating files for input redirection

A file used for UNIX input redirection (using the < symbol after the name of a program being run) is just a text file which you can create with any UNIX text editor (e.g., emacs). You type the exact lines to be used for the program's input the same way you would have typed them from the keyboard while the program was running if you were not using input redirection. To run the program with different input you can modify the file or create a new one with different contents.

The newline character will not be visible at the end of each line of the input file you create. It is necessary that there be a newline character at the end of the last input line, so be sure you press the return (or enter) key at the end of the last line of any file you create containing input values you are going to test your program with. Otherwise your program may not work properly in some circumstances.

7.4 Program debugging

  1. If your loops don't work as you expect, add debug printf statements. Since you are writing a program to draw something, the debug printf output will prevent your output from being displayed correctly, but it can help you figure out why your program is wrong and the debug printfs can be easily removed after that.

  2. If your program just stops and doesn't produce any results, it has either paused to wait for input from the user or you have an infinite loop. Another symptom of an infinite loop is a program which keeps printing the same thing over and over. Since your program will contain many loops you may not be sure which one causes the error. If you add a different debug printf statement inside the body of each loop and run your program again, the printf which gets repeated identifies which loop is the infinite one. If no line gets repeated, the infinite loop was either missed when you added the debug printfs or this loop does not have a body. An extra (unwanted) semicolon in the wrong place can cause the loop to have a null (empty) statement for its body.

  3. For technical reasons not worth explaining in full detail here, not all of your program's output will appear on the screen (or redirected output file) until a newline is printed. When a program produces output it isn't displayed directly on the screen. For efficiency and other reasons, output generated is saved internally (by the operating system) until a certain amount is present, and it's then all printed. This means that if a program contains an infinite loop, or has a fatal error, you may not see the results of the most recent output statements. You might think the program is having trouble at one point because it contains some printf statements and you didn't see their results printed, so the problem would seem to be above that point in the program. However, it could be that those statements were executed, but their results were just not displayed on the screen because the infinite loop or fatal error occurred soon afterwards in the program.

    It may sound like it's a difficult debugging problem to even figure out where in your program an error occurs, if printf results may or may not appear on the screen, but there is an easy way to see all of a program's output at any time. If a newline character (\n) is printed, then any pending output which has not actually been displayed yet will be immediately printed. So if your program seems to have an infinite loop (or a fatal error), either simply print some newlines, or even better, as mentioned above, add debug printf statements to every loop to see which one has the problem- but make sure each such debug printf ends in a newline character! Extra newlines or debug printf results will probably cause your output to appear incorrect, but at least they will help you figure out where your program's error is, and the extra print statements can be easily removed later.

  4. If you still can't figure out why your program doesn't work after you have thoroughly tried debugging it using these techniques, bring current printouts to office hours and we can teach you how to track the problem down.

    If there is any chance you may ever have to come to office hours, you should make your code readable from the very beginning. You should be able to easily understand it, and so should your instructor or a teaching assistant in office hours. If your code is a mess, the teaching assistants will direct you to first clean it up before returning so they can understand it and be able to help you. Naturally you want your code to be clear and easily readable by the graders after you have submitted it as well.

8 Academic integrity statement

Any evidence of unauthorized use of computer accounts or cooperation on projects will be submitted to the Student Honor Council, which could result in an XF for the course, suspension, or expulsion from the University. Projects are to be written INDIVIDUALLY. For academic honesty purposes, projects are to be considered comparable to a take-home exam. Any cooperation or exchange of ideas which would be prohibited on an exam is also prohibited on a project assignment, and WILL BE REPORTED to the Honor Council.


VIOLATIONS OF ACADEMIC HONESTY INCLUDE:


  1. failing to do all or any of the work on a project by yourself, other than assistance from the instructional staff.

  2. using any ideas or any part of another student's project, or copying any other individual's work in any way.

  3. giving any parts or ideas from your project, including test data, to another student.

  4. having programs on an open account or on a PC that other students can access.

  5. transferring any part of a project to or from another student or individual by any means, electronic or otherwise.


IT IS THE RESPONSIBILITY, UNDER THE UNIVERSITY HONOR POLICY, OF ANY STUDENT WHO LEARNS OF AN INCIDENT OF ACADEMIC DISHONESTY TO REPORT IT TO THEIR INSTRUCTOR.

9 Submitting your project

Turn in your program using the ``submit'' program as before, except using ``3'' for the project number. You are to submit only the .c file containing your source code, not the executable version of your program! If your program is in a file named p3.c, submit would be run as shown. Don't forget to read the class announcements in your instructor's account every time you log in.


% submit  3  p3.c

Before you submit your project, you must exactly follow the specific submission checklist in the ``Testing projects before submitting'' handout separately posted by your instructor!



Steve Scolnik 2003-03-08