Homework 2
User-defined functions: Modifying the craps game from Chapter 5

Due: Tuesday, November 7, 2006 at 11:59pm

Outcomes

After successfully completing this assignment, you will be able to...

Before Starting

Read Chapter 5, particularly sections 5.10 and 5.11. Make sure you thoroughly understand the program in Figure 5.10 before you start working on this assignment. To save yourself some typing time, you may want to copy the program in Figure 5.10 into your Unix directory (the program is available on the CD included with the textbook).

The Assignment

In this assignment you will modify and enhance the craps program introduced in Section 5.11. Your program will contain the following enhancements: The program will be modified so that the portion of the program that plays one game of craps will be packaged as a function. In addition, separate functions will be defined to read in and verify a wager, adjust the bank balance after a game is played, and read in a yes or no answer. Here are the specifications for each of the functions:

getWager asks the player to input a dollar amount to wager on the next game. The function checks the wager to make sure it doesn't exceed the player's current bank balance, and to make sure that it is greater than 0. As long as the wager is invalid, the player is asked to enter a new wager. Once a valid wager is entered, it is returned to the calling function.

playGame plays a single game of craps. It returns to the caller one of the enumerated constants WON or LOST. (Most of the code from Figure 5-10 will go into this function.)

adjustBalance This function either adds the wager to or subtracts the wager from the player's current balance, depending upon whether the last game played was WON or LOST.

getYesOrNo This function asks the player if he/she would like to play another game of craps. The function checks the response to make sure it is either 'y' or 'n'. The function will repeatedly ask for a y/n response until a valid response is entered. The answer (either 'y' or 'n') is returned to the calling function.

For each function you should write pre- and post-conditions, design the function as a black box (you don't have to turn in the black box), define a prototype, write a stub, and, once the program compiles successfully with each stub, fill in the function definitions (one at a time).

Include files

Assumptions and Restrictions

The main function should call getYesOrNo only as long as the player's balance is greater than 0 (once the player's balance goes to 0, the player is not allowed to continue).

Sample Execution

Balance = $1000.00
Enter wager:  100
Player rolled 5 + 6 = 11
Player wins

Balance = $1100.00
Do you want to play another game?  (y or n):  y
Enter wager:  1500
Your wager must not exceed your current balance.
Enter a new wager:  900
Player rolled 3 + 1 = 4
Point is 4
Player rolled 4 + 5 = 9
Player rolled 5 + 5 = 10
Player rolled 5 + 6 = 11
Player rolled 3 + 3 = 6
Player rolled 3 + 5 = 8
Player rolled 6 + 2 = 8
Player rolled 1 + 5 = 6
Player rolled 3 + 5 = 8
Player rolled 5 + 6 = 11
Player rolled 3 + 1 = 4
Player wins

Balance = $2000.00
Do you want to play another game?  (y or n):  q
You must answer y or n.
Do you want to play another game?  (y or n):  y
Enter wager:  2000
Player rolled 6 + 5 = 11
Player wins

Balance = $4000.00
Do you want to play another game?  (y or n):  n

Your final balance is $4000.00

A note about character input

This program will require a deeper understanding of how C does keyboard input. When reading in single characters (like y or n) it is usually easier to use the C function getchar instead of using scanf. getchar returns the next single character from the input stream. Look at the Sample Execution above. You would use a printf statement to output the prompt, "Do you want to play another game? (y or n): ". Now think of what the user types in response...not the single character y, but two characters, y and the ENTER key (the C constant '\n'). You can read in the y with the statement 
  ch = getchar();
That still leaves the newline character in the input buffer. This becomes a problem if the user had typed in an invalid response like q instead of y or n, because the next time you try to use getchar to read in a valid response it will read in the newline, not the user's new input value. Similar problems are encountered if you use getchar after reading in a numeric value; scanf reads in the characters for the numeric value, and leaves the next character to be read (the newline character) still in the input buffer. A quick way to fix this problem is to follow each input statement with the loop: 
  while (getchar() != '\n');
(Notice the placement of the semi-colon. The loop body is empty.) This loop essentially reads the rest of the characters on the line, and ignores them, until it reaches the end of the line. The next time your program executes an input statement (either scanf or getchar) it will get the input from the next line typed by the user. You may find getYesOrNo the most difficult function to write for this assignment. I suggest you get everything else working in your program first, then add the code that relies on getYesOrNo.

Deliverables

Submit your implementation file using the following turnin command:

/cs/bin/turnin submit cs2301 hw2 hw2.c

Programs submitted after 11:59pm on November 7 will be tagged as late, and will be subject to the late homework policy.

Grading

This assignment will be graded on the following areas: documentation (including pre- and post-conditions for all functions), proper choice of parameters and local variables, proper choice of function return types, adherence to specifications for each function, correctness, and robustness (ability to recover from invalid input). Programs must compile successfully in order to receive points for correctness.