Homework 4

Goal

The purpose of this assignment is to help you gain experience using conditional statements, loops, arrays, and pointers in C++.

Assignment

Part 1 - (5 points)

Implement a function with the following signature to return the number of days in the passed-in month argument.

int GetDaysIn(int nMonth, int nYear);

The function should return -1 if any of the arguments is invalid. Note that years evenly divided by 400 are leap years, unlike years otherwise evenly divided by 100. Your function must use at least one switch statement and at least one if statement to perform its work.

Implement the main() function for this program. This function must call GetDaysIn() repeatedly to fill an array of integers with values representing the number of days in each month of a particular year. The process of repeatedly calling GetDaysIn() to fill the array must be implemented using a while loop. Next, use a separate for loop to output the contents of the array to the screen. Do this for enough different test cases to ensure that GetDaysIn() always returns the correct results.

Part 2 - (5 points)

More fun with calendars...

Write a function that uses this formula to calculate and print the date of Easter for any given year.  Check to make sure that you get the right answer for 2002 (March 31).

Part 3 - (5 points)

Using function pointers:

• Use typedef to define a type (call it ACTION_FCN) for a function that takes an istream& argument and an ostream& argument and returns a bool.
• Define a struct called Action that contains the following elements: a char* called Command, and an ACTION_FCN called Function.
• Write the following ACTION_FCN's : GoNorth(), GoSouth(), Fight(), Get(), Quit(), and InvalidCommand(). Each function should output an appropriate message to its ostream& argument, such as "Going north...\n". Get() should read a word from its istream& argument and display "Getting the <foo>\n", where <foo> is that word. Each function should return true, except for Quit(), which should return false.
• Write a function named ExecuteCommand() that takes a string argument, an istream& argument, and an ostream& argument and returns a bool. This function should define a local variable called Actions that is an array of Action objects and initialize it so that it contains the following elements:

  "look"	Look
  "l"	Look
  "north"	GoNorth
  "n"	GoNorth
  "south"	GoSouth
  "s"	GoSouth
  "fight"	Fight
  "f"	Fight
  "get"	Get
  "g"	Get
  "quit"	Quit
  "q"	Quit
  ""	InvalidCommand

  There is a simple and elegant way to initialize this array in the declaration statement. See if you can find it.
• Declare a variable named pAction that is a pointer to Action and initialize it to point to the first Action in Actions.
• Use a while loop that loops until pAction->Command matches the passed-in string or pAction->Function is InvalidCommand. Use ++ to move from one Action to the next.
• When the loop exits, call pAction->Function with the istream& and ostream& arguments you passed in, and return whatever it returns.
• Finally, write a main() function that uses a do ... while loop to prompt for a command on cout, read the command from cin and call ExecuteCommand() with the command, cout, and cin as arguments. Loop until ExecuteCommand() returns false.

Does this look like anything you might be able to use later???

Part 4 (5 points)

Consider the following code fragment:

int nVal = 7;
int* pVal1 = NULL;
int* pVal2 = NULL;

Assume that the following set of assignment operations are executed in sequence. Which of these assignment operations are safe? Which are not? Explain each answer.

pVal1 = nVal;
pVal1 = &nVal;
pVal2 = pVal1;
nVal = pVal2;
pVal1 = 20;
*pVal1 = 20;
nVal = 20;

Note that you do not need to define any classes for this assignment!

Deliverables

Put your program files for Parts 1 and 2 and a file named part3.txt containing your answers to Part 3 into an archive file named hw3.zip or hw3.tar.Z.  Save this archive file in your AISYG 240 course directory (Courses/AISYG 240) on ftp.coe.neu.edu.