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Programming Paradigms

Lecture one deal with the following Programming paradigms:

 HYPERLINK "http://www.desy.de/gna/html/cc/Tutorial/node3.htm" \l "SECTION00310000000000000000"  Unstructured Programming
 HYPERLINK "http://www.desy.de/gna/html/cc/Tutorial/node3.htm" \l "SECTION00320000000000000000"  Procedural Programming
 HYPERLINK "http://www.desy.de/gna/html/cc/Tutorial/node3.htm" \l "SECTION00330000000000000000"  Modular Programming
 HYPERLINK "http://www.desy.de/gna/html/cc/Tutorial/node3.htm" \l "SECTION00360000000000000000"  Object-Oriented Programming
Unstructured Programming
Usually, people start learning programming by writing small and simple programs consisting only of one main program. Here ``main program'' stands for a sequence of commands or statements which modify data which is global ((عامة اي متاحة لكل البرنامج throughout the whole program. It could be illustrated as shown in Figure 1.

Figure 1: Unstructured programming. The main program directly operates on global data.

This programming technique provides many disadvantages (مساويء) once the program gets sufficiently large. For example, if the same statement sequence is needed at different locations within the program, the sequence must be copied. This has lead to the idea to extract these sequences, name them and offering a technique to call and return from these procedures.

Procedural Programming

With procedural programming you are able to combine returning sequences of statements into one single place. A procedure call is used to invoke the procedure. After the sequence is processed, flow of control proceeds right after the position where the call was made (Figure2).


Figure 2: Execution of procedures. After processing flow of controls proceed where the call was made.With introducing parameters as well as procedures of procedures (sub-procedures) programs can now be written more structured and error free. For example, if a procedure is correct, every time it is used it produces correct results. Consequently, in cases of errors you can narrow your search to those places which are not proven to be correct. Now a program can be viewed as a sequence of procedure calls. The main program is responsible to pass data to the individual calls, the data is processed by the procedures and, once the program has finished, the resulting data is presented. Thus, the flow of data can be illustrated as a hierarchical graph, a tree, as shown in Figure 3 for a program with no sub- procedures.



Figure 3: Procedural programming. The main program coordinates calls to procedures and hands over appropriate data as parameters. Now we have a single program which is divided into small pieces called procedures. To enable usage of general procedures or groups of procedures also in other programs, they must be separately available. For that reason, modular programming allows grouping of procedures (مجموعة من الاجراءات) into modules.

Modular Programming

With modular programming procedures of a common functionality are grouped together into separate modules. A program therefore no longer consists of only one single part. It is now divided into several smaller parts which interact through procedure calls and which form the whole program (Figure 4). Each module can have its own data. This allows each module to manage an internal state which is modified by calls to procedures of this module. However, there is only one state per module and each module exists at most once in the whole program.


Figure 4: Modular programming. The main program coordinates calls to procedures in separate modules and hands over appropriate data as parameters.
Object-Oriented Programming
Object-oriented programming solves some of the problems just mentioned. In contrast to the other techniques, we now have a web of interacting objects, each house-keeping its own state (Figure 5). In object-oriented programming we would have as many objects as needed. Instead of calling a procedure which we must provide with the correct object handle, we would directly send a message to the object in question. Roughly speaking, each object implements its own module allowing for example many objects to coexist. Each object is responsible to initialize and destroy itself correctly. Consequently, there is no longer the need to explicitly call a creation or termination procedure.


Figure 5: Object-oriented programming. Objects of the program interact by sending messages to each other.
You might ask: So what? Isn't this just a modular programming technique? You were right, if this would be all about object-orientation. Fortunately, it is not. Beginning with the next lectures additional features of object-orientation are introduced which makes object-oriented programming to a new programming technique.
H.W.
Design a Library system based on all three programming paradigms.










2nd class Lect 1/OOP

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