Program Development and Programming Languages

1. Lecture 4 Program Development and Programming Languages Reference :Understanding Computers Chapter 13

2. The Program Development Life Cycle • Creating new programs is called program development. • The process associated with creating successful applications programs is called the program development life cycle (PDLC).

3. The Program DevelopmentLife Cycle (PDLC) • Program Development (application software development) • The process of creating application programs • Program Development Life Cycle (PDLC) • The five phases of program development

4. 1- Problem Analysis • During problem analysis, a systems analyst and programmer review specifications and talk with users to fully understand what the software should do. • Documentation consists of: • program specifications, • timetable, • which language will be used, • how the program will be tested, • and what documentation is required.

5. 2- Program Design • Program design:stage where program specifications are expanded into a complete design of the new program. • Structured programming and object-oriented programming are two of the most significant approaches to the design process.

6. Program Design: Program Design Tools Program design tools are planning tools. • Structure charts • Program flowcharts • Pseudocode

7. Program Design: Program Design Tools 1-Structure charts show the overall organization of a program, and how the modules of a program—logically related operations that perform a well-defined task—are defined and how they connect to each other hierarchically. Program modules should be arranged hierarchically, in a top-down fashion, so that their relationship to each other is apparent.

9. Program Design: Program Design Tools • 2-Program flowcharts • use geometric symbols and familiar relational operators to provide a graphic display of the sequence of steps involved in a program. • The steps in a flowchart follow each other in the same logical sequence as their corresponding program statements will follow in a program. • Different symbols are used to represent different actions, such as start/stop, decision, input/output, processing,and looping symbols.

12. Flowcharts

13. Flow chart Example Start Input Expenses E Yes E<1000? Subtract Expenses R <= 1000-E No Print You Owe $0 Print You Owe $R Stop

14. Program Design: Program Design Tools 3-Pseudocode uses English-like statements in place of the graphic symbols of the flowchart. Unlike a flowchart, pseudocode is easy to modify and can be embedded into a program as comments. No standard set of rules exists for writing pseudocode, although a number of conventions have been developed.

16. Program Design: Control Structures • Sequence • Selection • Iteration

17. . . . Statement Statement Statement Program Design: Control Structures Sequence A sequence control structure is simply a series of procedures that follow one another.

18. True Statement1 Statement Condition . . . Statement2 False Program Design: Control Structures Selection ·The selection (if-then-else) control structure involves a choice: if a certain condition is true, then follow one procedure; else, if false, follow another. When more than two possible choices exist, the case control structure can be used instead.

19. Statement Program Design: Control Structures Iteration • loopis an operation that repeats until a certain condition is met. • A looping (iteration) control structure can take two forms. • With the do-while structure, the loop is executed as long as a condition is true; with the do-until structure, the loop continues until a certain condition becomes true. False . . . Condition True

20. Program Design: Good Program Design nGood program design is essential; it can save time and it produces a better end result. Some principles of good program design are: • Be specific • One-entry-point, one-exit-point rule • No infinite loops • Documentation during program design includes all the design specifications

22. 3- Program Coding • Coding: actual process of creating the program in a programming language. • Programming language must be chosen. • Codingstandards should be adhered to. • Make use of reusable code and data dictionaries. • Translate coded programs into executable code. • Documentation results in finished source code.

24. Program Coding • nThe coded program is referred to as source code. • to be executed, the program is converted by the computer to object code using a special program. • A compiler translates the entire program into machine language before executing it. The program then doesn’t need to be recompiled until it is modified. • An interpreter translates program statements one at a time. Interpreters are helpful during the debugging stage, but are slower during execution of the finished program. • An assembler converts assembly-language statements into machine language.

25. 4- Program Debugging and Testing • Debugging:process of making sure a program is free of errors or bugs. • Preliminary bugging often finds syntaxor logicerrors. • Testing can consist of alpha or beta testing. • Documentation includes a copy of the finished program code, plus test data and results.

26. Program Debugging and Testing • Preliminary debugging begins after the program has been entered into the computer system. Rarely is a program error-free the first time it runs. Two common types of errors are syntax errors and logic errors. • A syntax error occurs when the programmer has not followed the rules of the language. • A logic error, or execution-time error, results when the command syntax is correct but the program is producing incorrect results.

27. Program Debugging and Testing • At some point in the preliminary debugging process, the program will appear to be correct. At this point, the programmer, or preferably someone else, will run the original program with extensive test data. • Good test data will subject the program to all the conditions it might conceivably encounter when finally implemented. • Most companies run on-site alpha teststo test programs; companies in the business of selling software also commonly run beta testsby distributing preliminary versions of the program to outside users.

28. 5- Program Maintenance • Programmaintenance: process of updating software so that it continues to be useful. • A costly process, but can be used to extend the life of a program. • Documentation consists of amended program package reflecting what problems occurred and what program changes were made.

29. What Is a Programming Language? A programming language is a set of rules used to write instructions to the computer.

30. Categories of Programming Languages • Low-level languages • High-level languages • Fourth-generation languages (4GLs) • Natural and visual languages

31. Categories of Programming Languages • Machine and assembly languages are called low-level languages, because programmers who code in them must write instructions at the finest level of detail, the base level of the hardware. • Although virtually no one writes machine-language programs anymore, all programs must be translated by a language translator into machine language before they are executed. • Assembly languages are fast and consume little storage when compared with higher-level languages, but take longer to write and maintain.

32. Categories of Programming Languages ·High-level languagesdiffer from their low-level predecessors in that they require less coding detail and make programs easier to write. Programs written in a high-level language (BASIC, COBOL, Pascal, C, etc.) need to be translated into machine language before they can be executed.

33. Categories of Programming Languages ·Very-high-level languages, also known asfourth-generation languages (4GLs), are much easier to use than the high-level languages that preceded them, because they are declarative rather than procedural languages. For instance, to draw a bar chart in a procedural language, you must tell the computer how to draw bars and where to place them. In a declarative language, you may be able to just point to the data you want graphed, click several menu choices, and you’re in business. Fourth-generation languages are commonly used to access databases (query languages).

34. Popular Programming Languages • FORTRAN • COBOL • Pascal • BASIC and Visual Basic • C, C++, and C# • Java

36. Markup Languages • Markup languages use symbols or tags to describe what a document should look like when displayed. • HTML (Hypertext Markup Language) • Dynamic HTML • XML(extensible markup language) • XHTML (extensible Hypertext Markup Language) • WML (Wireless Markup Language )

38. Scripting Languages • Scripting languages are used to build program instructions into Web pages, usually to add dynamic content. • JavaScript • VBScript • Perl