CSE2305 - Object-Oriented Software Engineering
Assessment

Assignment 2

Synopsis

• Question 1
• Question 2
• How to Proceed
• What to submit for assessment

Question 1

An associative array is an array that stores one data type (the value) indexed by another (the key). This is a generalisation of the standard array in C which only allows indexing by a number. For example:

postcode["Clayton South"] = 3068;
cout << "The postcode for " << cityName << " is " << postcodes[cityName] << endl;

Write a class^¤ called Array which implements an associative array.  The key for the array will be a std::string.  Elements stored in the array will contain data, also of type std::string. Your Array class should be able to store any number of elements. The example above uses operator overloading to overload operator[]. For this assignment, there is no need to overload operators, so member functions will be used to get and set the data.

Your Array class^¤ should provide the following methods:

• A default constructor^¤ which initialises the (empty) Array object.
  
• A destructor^¤ (but only if one is required)
   
• A member^¤ function^¤, Array::Insert(string key, string value), which inserts the specified value into the array using index key.
  
• A member^¤ function^¤, Array::Delete(string key), which deletes the specified key and the value associated with it.
  
• A member^¤ function^¤, Array::Exists(string key), which searches for the specified key and returns true if the key was found and false otherwise.
  
• A member^¤ function^¤, Array::Find(string key), which searches for the specified key and returns the data associated with the key (if it exists), or a null string otherwise.
   

Classes^¤ such as the List and Array classes^¤ are called Containers^¤.  Container Classes^¤ are used to store any type of data.  Consider for the future how you could specify and store arbitrary data types for the key and value.

Question 2

Using the Array class¤ you implemented in the previous question write a class¤ called PostCodeFinder, which can load a list of postcodes stored in a file, and then be used to find the postcode for the supplied city name and state.

Your PostCodeFinder class¤ should provide the following methods:

• A constructor¤ which takes a filename and loads the corresponding word list into an encapsulated Array data member¤¤

• A destructor¤ (but only if one is required)

• A member¤ function¤, PostCodeFinder::Lookup(string cityName, string state), which returns the postcode for the city if it exists, an empty string otherwise.

Use your PostCodeFinder class¤ to write a simple post code lookup program. The program should load a list of cities, states and postcodes from a specified file into a PostCodeFinder object, then prompt for a city and state name, returning the corresponding postcode if found, or the string "No postcode found for cityname" (where cityname is the name of the city entered). This should repeat until the user terminates the cycle. The program then quits.

How to Proceed

Associative arrays are best implemented as a hash table. You will need to devise a suitable hash function to hash a string key to the appropriate position in the array.

Hash tables need to handle collisions (when two different keys hash to the same location).  To handle collisions, make sure your Array class^¤ stores a List of elements at each location in the array (see Assignment 1).

What to submit for assessment

You should submit the following:

• All source code necessary for this assignment.
• Test data required by the software.
• A Makefile, with 2 targets: the default target builds the program(s), the clean target removes the executable and any intermediate (e.g. .o files created during compilation).
• A plain text README file briefly explaining what you have done (including testing) and how to perform the tests on your submission.
• Written components of the assignment should be done in plain text (i.e. readable using a standard text editor such as vi).

See the submit page for details on how to submit your assignment.

Last Modified: August 24, 2005