Purpose:

This assignment will explore the issues of identifying objects in a problem statement and implementing small abstract data types, using the C++ struct..

The key is to have the data structures separate from the functions that manipulate them, as described below.

What to hand in:

Hand in descriptions of the objects requested with text or diagrams corresponding to your favorite object-oriented documentation techniques. UML, Booch, CRC, and all other methods are acceptable.

For the programming assignment, hand in a listing of the program (which must be formatted in a reasonable style), and sample run(s) of the program. Choose sufficient test cases to ensure your functions work properly.

Problems:

Think about time:

1. Consider the concept of a Date. This object will have several uses; the one we will keep in mind is for a ledger or billing system (the date is important, but not time of day).

2. Define the object, a set of logical attributes, and its responsibilities.

3. Document the object in a manner you have learned in the OO course.

4. Please implement at least the following functions related to a date:

• print the date instance

• get (return) the day of the month from a date instance

• get (return) the year from a date instance

• get (return) the month from a date instance

• set the date instance to a given value

• validate the date instance (return true (1) or false (0))

• set the date instance to "now"

5. Implement and test this data type as a struct.

6. Be sure to create a header file that describes the type and at least one implementation file to provide the services. A separate file should provide the testing. .

Use time(), localtime(), strftime() or asctime() to add the idea of "now" in implementing Date. These are all expressed in <ctime>

Remember the goal is to implement a date type and operations to manipulate it!

Notes:

The goal of the exercise is to think in object-oriented terms. Your Date structure serves the role of the object in Object oriented terms (and is declared in the date.h file):

struct Date

{

int month;

int day;

int year

}; /* One implementation (there are others) */

The variables of that type serve the roles of instances of the object:

Date d1, d2, d3; /* Mostly found in the test main program */

Thus, each of the functions should manipulate the instances of the object–they are the messages of the object-oriented paradigm. The message interface is defined in the date.h file:

void DatePrint ( Date *);

int DateDay ( Date *);

int DateMonth ( Date *);

int DateYear ( Date *);

int DateSet ( Date *dp, int mon, int dy, int yr);

int DateValid ( Date *);

int DateNow ( Date *dp);

Note that this approach entirely isolates the clients of your code from the internal details: where you might have had a piece of client code (in, say, testmain.c) like:

Date d1;

d1.month = 3;

d1.year = 1995;

d1.day = 31;

print ( "%d/%d/%d\n", d1.month, d1.day, d1.year);

which is dependent on your representation. You will now have code in testmain.c like:

Date d1;

DateSet (&d1, 3, 31, 1995);

DatePrint (&d1);

Functions become simpler and smaller. The function DateSet, for example, in date.c, may resemble:

int DateSet ( Date *dp, int m, int d, int y ) {

dp->day = d;

dp->month = m;

dp->year = y;

return DateValid(dp);

}

Some become trivial. For instance, DateDay is supposed to return the day of the month for this Date:

int DateDay ( Date *d)

{

return d->day;

}

While identifying important objects and attributes, consider what techniques you’ve learned that make your life easier as a designer and implementor. Consider different methods of selecting objects (e.g., noun parsing, category prompts): which worked better for these very short problems?

The function time_t time(time_t *t) returns the number of seconds since 1 Jan 1970 GMT on Unix systems. The function struct tm *localtime(time_t *t) takes (the address of) this result and converts it into a structure with tm_month, tm_day, tm_year, etc. as components. The function time_t mktime (struct tm*) takes one of the time structures, completes it reasonably, and returns the equivalent seconds count.

A function to set the date to the current time may look as follows:

int DateNow ( Date *dp) {

time_t t = time(0L); /* Stores the current time in t */

struct tm *tp;

if (t == (time_t)(-1))

return 0;

tp = localtime(&t); /* Turns t into a struct tm */

dp->day = tp->tm_mday;

dp->month = tp->tm_mon + 1; /* Perversely, months are 0-11 */

dp->year = tp->tm_year + 1900; /* struct tm uses 2-digit years */

return 1;

}

Evaluation Criteria:

Code will be evaluated both for proper style and for correct content. Your code should be in 3 (or more) files: date.h, date.cpp, and testdate.cpp (date.cpp could be subdivided into many other files if you choose).