CMSC 106 Project #5 - Gem Drop 2.0 Spring 2003


Due date: Sunday, April 20 at 11:00 pm

1 Purpose

In this project you will write a program which uses functions in addition to arrays.

You will write another gem drop game, but this time there can be up to 10 players at the same time. Most of the rules of the game will be the same as the 1-player game, but there will be some important differences.

Since much of the description of this project is identical to the previous project, we will omit many details. You may need to refresh your memory by reading through the description of Project #4 before reading this project description.

2 Files Provided

Like the previous project, we will provide you with the following files:

gemdrop2.x  (the executable)
primary_input
primary_output

3 Project Desciption

3.1 Input Files

The input for this program will be somewhat different from the previous project. Below is the primary_input file that we have given you:

5 6 2
Ruby     2
Emerald  1
Topaz    3
Diamond  4
Sapphire 10
Amethyst 7
Gold     5
Jade     8
end
1 R 0
1 G 1
2 G 2 
2 S 1
2 S 2
1 T 3
1 E 0
1 S 1
2 S 2
1 T 3
1 G 0
1 T 1
1 T 2
2 G 1
1 G 2
1 T 3

As before, the first two numbers represent the number of rows and columns for the game board. (The maximum possible size is still 30 rows and 30 columns). The third number is the number of players. The moves are given by the letter of the gem and the column number as before, but each move is preceded by the number of the player making the move. (Notice that the players are numbered starting with 1, not 0, and the players do not necessarily move in numeric order.)

Important: Your program will use one or more arrays to keep track of the game board and players' scores. For example, in your previous project you probably had an integer variable to keep track of the score. In this project, you will need a whole array of integer values to keep track of the scores for all of the players. You will probably have several arrays that will hold various pieces of information about the game board.

3.2 Error Checking

In addition to the error checking done in Project #4, there is some error checking related to the multiple players.

3.3 Playing the Game

Processing the game moves is similar to that in the previous project, but now the gems are "owned" by the player who placed them on the board. If a group of gems are removed by making a match, the player who made the match receives the points for the gems which are removed as before. The points for the removed gems are now also DEDUCTED from the score of the player or players who originally placed the gems on the board. (This means that a score could become negative.) If a gem was placed on the board by the same player who removes it, then the points are just added to that player's score.

Another important difference in this version of the game is that matches can be made for 3 or more adjacent gems, even if they are not in the same horizontal or vertical line. (This is the same rule as in the graphics version of the game on the Web.) For example, the following patterns would result in a match for gem X:

....  
....
EXX.
RRX.

....
....
.AXX
.RXA

etc.

Note that the gems must still be adjacent vertically and/or horizontally, not diagonally, so this would NOT be a match:

....
..X.
AXE.
XAA.

3.4 Processing

In the previous project it was suggested that the main body of your program should be a big loop, where each pass through the loop represents one move in the game. This is still the correct approach. Now, your main function should be very short, since the real work of the program will be done in other functions which are called by main and by each other.

The moves will be processed until the game ends as before. The program will then print out the final appearance of the game board and a list of the scores for each player.

Any other requirements and tasks your program had to perform in Project #4 still apply to this project, even if they are not mentioned above, unless specifically contradicted or modified here. As in the previous project, you may want to use ``usleep'' to slow the computer down. If you do, be sure to remove all calls to usleep before submitting your project!

4 Required functions and implementation

This program must be implemented using many small functions.

Failure to comply with the above will result in a project grade of no more than 50 points out of 100.

Furthermore, you must provide a function prototype for every function in your project (other than ``main'').

Many of your functions may call other functions you have written. You should write and test each function separately, starting with the simpler ones, before implementing those which could depend upon them. You may use ANY function names that you choose. To get you started, here are a few suggestions. (You do not have to use ANY of these, and you will probably need more functions.):

   initialize_game_board
   create_gem_list
   check_move
   find_match
   remove_match
   annihilate
   adjust_score
   print_board

Again, these are only suggestions to get you started. You can use whatever functions you choose. Keep in mind that some of your functions will need to call other functions.

5 Checking Your Outputs

You should use the ``diff'' command to check your output for the primary case. For this project, you should use ``diff'' without specifying ``-bwi''.

6 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. Prototypes must appear for all functions used, and at most one return statement may be used in any function. Even if you already know what they are, you may not use any C language features other than those introduced in Chapters 1 through 9 of your textbook, plus those presented in lecture while these chapters were covered. In addition neither the goto nor the continue statement may be used, and the break statement may not be used to terminate a loop. Your program may not use the exit() library function at all. You must use character constants (i.e., 'A'), rather than numeric ASCII values anywhere character values are needed. Lastly, no global variables may be used. Using C features not in these chapters, or using global variables, the goto statement, the exit() library function, 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. In addition, you must have a short comment before each function explaining its action and operation. 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:


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.

Because this project is larger than the previous projects, being able to determine what part of your code is causing an error is much more important. If you need to come to office hours, you will be expected to be able to tell us where the error is, or what you have done to try to locate it. This means having tested your functions, as explained below, so that you know which ones already work for sure. It also means it is absolutely necessary to develop your program in stages so that you are not trying to write and test all of the code at one time.

7.1 Program development strategy

As discussed in the earlier project assignments, it is very important to type in only a part of your program at a time and compile and test it, and verify that it is correct, before going on. For a program with functions, this means writing only one function at a time. It also means making sure that function is correct before calling it from your main function or another function. The way to determine if it is correct or not is to add test calls, or temporary statements just for the purpose of testing this function, to your program. You can add these calls at the beginning of your main function. The idea is that, having written a function, you know what it is supposed to do. Call it passing some sample values as arguments and print its return value if it has one, to make sure that it does its whatever it was supposed to do correctly. If it's supposed to change some values in an array, print the array after the test call to insure the function did what it should have. You should be able to figure out by hand what results the function was supposed to produce for the call you wrote. If it doesn't do what you think it ought, you need to find out why before going on!

It may be best for you to implement the shorter functions first. After you write and test these you will have more practice with functions, and can go on to write those which are a little more complex.

Due to the complexities of reading character input, and the possibility of error which may occur, it's extremely important to carefully print the input values which your program reads to insure it's reading its input data correctly! Often one of the first steps of writing a program can be to simply write the code which reads the input and test it by printing the input values as they are read, because if the input isn't read properly clearly no code after that will be able to work right, even if written correctly.

7.2 Finding compilation errors

Here are several common compilation errors having to do with functions produced by the cc compiler on our class machines and what they mean:


In this declaration, the type of ``X'' is not compatible with the type of a previous declaration of ``X''

(where X is the name of one of your functions, and this error occurs where the function is declared)

This means you called a function before it was defined, or before the compiler saw a prototype for it. The solution is to add a prototype for every function at the top of the program file as soon as it is written, which tells the compiler everything it needs to know about the function so it won't become confused in this way.

In this declaration, the number of parameters differs from an earlier declaration of this function

The function as written has a different number of parameters than the prototype which you wrote for it.

Non-void function ``X'' does not contain a return statement

You wrote a function which you specified should have a return value, but you didn't include a return statement anywhere inside it. If you want the function to return a value, you have to add a return statement. Or, if you don't need it to return anything after all, change its declaration to indicate that it doesn't return anything.

In the declaration of ``X'', the array bounds are incorrectly specified

(where X is the name of a two-dimensional array parameter in one of your function definitions)

You can omit the first subscript of a two-dimensional array parameter when defining a function, but not the second one. This error is usually caused by trying to write a two-dimensional array parameter with two empty sets of brackets, such as arr[][]. The number of columns must appear inside the second set of brackets.

In this statement, ``X'' does not point to an object type

(where X is the name of an array parameter in some function)

This is typically caused by the same problem as the previous error.

7.3 Program testing

Just because a function works correctly for one or two sets of inputs doesn't mean it always works right. You will need to think of a variety of different possibilities for the function's input values (arguments) and make sure it produces the right results in every case. A few minutes spent adding statements which test each function with varying values will be well worth it, if it saves you hours of trying to track down a bug later! Once you are convinced your function works correctly, just delete the test calls, and integrate the new function into the rest of your program by calling it where it is needed.

To illustrate the fact that correct results in one or two cases don't mean a function always works correctly, imagine that for some program you have to write a function which counts how many times a given number is located inside an array containing 10 integers, and returns the result. Its parameters are an array of integers and the value which should be searched for inside the array. Here is the function you wrote:


int count_quantity(int arr[], int num) {

  /* This function returns the count of how many occurrences of its
   * second parameter are found in its first array parameter.  The
   * array is assumed to have ten elements.
   */

  int count= 0, index= 1;

  while (index < 10) {

    if (arr[index - 1] == num)
      count++;

    index++;
  }

  return count;
}


To test this function you could write a small main function containing an array, call the function with that array and a value to search for inside it, and print the answer which was returned. You can tell what results it should produce from examining the array. For example:

int main() {
  int array[10] = {3, 1, 5, 1, 4, 7, 9, 4, 2, 1};

  printf("number %d was found %d times\n", 3, count_quantity(array, 3));
  printf("number %d was found %d times\n", 4, count_quantity(array, 4));

  printf("%d\n", count_quantity(array, 4));

  return 0;
}


You would see that the first test call returns and prints 1, and there is in fact only one 3 inside the array. The second one prints 2, and there are two 4s in the array. You might conclude that your function was correct, however, this is not the case! Altering the call to search for different values, or adding separate test calls, reveals that the call:


printf("number %d was found %d times\n", 1, count_quantity(array, 1));
          


would also print 2, however, there are three 1s in the array, therefore 3 should be the correct result printed! The problem is that the last array element is never examined, since the loop stops immediately when index reaches 10, and arr[8] was the last element tested. You could verify this by adding a debug printf statement in the loop printing each array element as it is examined. In this case, changing the loop condition to ``while (index < 11)'' would be one way of fixing the problem.

The crucial point is that testing the function by calling it in only a few cases is not sufficient to conclude that it is correct.

7.4 Program debugging

If random or unexpected values are printed some of the most common reasons are:


  1. One of your loops is examining elements which don't belong to the array (it has gone off either side of the array). Trace your code by hand with a diagram of the current values of the array, or add debug printf statements to see the values of the array subscripts which you are using, to see where the error might be happening.

  2. You have a function which returns values in some cases but not in others. This can be avoided by using only one return statement at the end of each function (as required above) to pass back a value which was computed or determined, rather than several return statements in different places in the same function.

  3. You may be printing or using values of variables which were not initialized. Initialize all variables, or print the value of each variable before using it, to see where you are using one that hasn't been initialized.

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

Be sure to remove all calls to the usleep function before submitting your project! Your project must be electronically submitted by the date above, to aviod losing credit as described on the syllabus. No projects more than two days late will be accepted for credit without prior permission or a valid medical excuse, as described on your syllabus. Only the project which you electronically submit, according to the procedures provided, can be graded; it is your responsibility to test your program and verify that it works properly before submitting. Lost passwords or other system problems do not constitute valid justifications for late projects, so do not put off working on your program or wait to submit it at the last minute!

Turn in your assignment using the ``submit'' program as before, except using ``5'' 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 ``p5.c'', submit would be run as submit 5 p5.c.



Steve Scolnik 2003-04-10