Different Programming Paradigms

• Procedure-oriented programming: This approach uses many procedures to carry out the computation. There is a global pool of data that the procedures update.

  The danger of this approach is that as the program gets large, it is difficult to keep track of which routines are changing the common data and how. This makes the program difficult to modify and prone to bugs.

• Copy data to routines: A second approach is for the data to be allocated and controlled by the main routine. The main routine passes to routines the data that the routine will need. The routine modifies this data and passes it back to the main program.

  If done well, this can solve the problem of not knowing how each routine changes the common data. The problem with it is that it requires a great deal of information to be copied. The programming language Pascal typically uses this approach.

  For an example, see the code included in the assignment. The main program declares two variables, bigSpenderNames and competitorCustomerNames (click for location in code). Each of these consists of an integer and twenty strings. The routines in the module StringList modify these variables. (The data type StringList.listType is defined in the module StringList, but this does not allocate any memory. Note that this type is exported by the module so that main program can uses it.)

• Passing Pointers: In order to avoid copying the data back and forth between routines, one can use pointers. As above, the data is allocated and controlled by the main routine. Here, however, routines are only passed pointers to the data.

  Pointers are a key tool in the programming language C. People just learning to program often find passing pointers to and from routines causes them grief. To avoid these problems, OOT handles this automatically. When a formal parameter in a procedure is not of a simple type (eg char, integer, or pointer), then instead of copying the value of the parameter into the procedure, a pointer to the data structure is passed. The first question of this assignment will give you some understanding how pointers are passed.

• Abstract Data Types (Information Hiding): When programs get large it is helpful to build separate modules to perform certain tasks. It is useful to separate out the logical properties of the module from its implementation. In this way, the module and the programs that use the module can be written and modified without understanding of the implementation details of the other. In this paradigm, the data for the module is global to the routines in the module, but is hidden from the rest of the program. The rest of the program accesses the data only via routines within the module.

  The code included in the assignment includes an example of this. The module Transactions allocates the data structure Trans. This is data is not exported. Hence, the main routine has no access to it, except via the routines that are exported.

  The disadvantage of having the data local to the module is that the main routine is restricted to having only one instance of this module. In contrast, the main routine allocates space for two lists of strings, bigSpenderNames and competitorCustomerNames, which can be passed to the same module StringLists.

• The Object Oriented Paradigm: A new paradigm is that software should be constructed out of parts, called objects. These re to be designed so that they are easy to understand, to use, and to re-use. An object consists of a set of data structures, together with the operations that can be performed on this data. Objects that are similar are collected into classes, and classes are organized into hierarchies. Objects from one class can inherit characteristics or attributes from the class that is its parent in the hierarchy of classes. This allows the programmer not to have many copies of similar code in the same program.

  The example code includes two modules, StringList and TransationList . Each module handles a single list, one of strings and the other of credit card transactions. Other then this difference, the code for the two modules are very similar.

  A main part of this assignment is to write a single class of object called IntList. This will have all the code for handling lists. You will also write the derived classes that inherits everything from IntList except what it is a list of.