Copyright © 2003 by Prentice Hall Computers: Tools for an Information Age Chapter 15 Programming and Languages: Telling the Computer What to Do

2Copyright © 2003 by Prentice Hall Objectives Describe what programmers do and do not do Explain how programmers define a problem, plan the solution, and then code, test, and document the program List and describe the levels of programming languages: machine, assembly, high level, very high level, and natural Describe the major programming languages that are in use today Explain the concepts of object-oriented programming

3Copyright © 2003 by Prentice Hall Programming Program – a set of detailed, step-by-step instructions that directs the computer to do what you want it to do Programming language – a set of rules that provides a way of telling the computer what operations to perform

4Copyright © 2003 by Prentice Hall The Programming Process Five main steps Defining the problem Defining the problem Defining the problem Defining the problem Planning the solution Planning the solution Planning the solution Planning the solution Coding the program Coding the program Coding the program Coding the program Testing the program Testing the program Testing the program Testing the program Documenting the program Documenting the program Documenting the program Documenting the program

5Copyright © 2003 by Prentice Hall Defining the Problem Develop a written agreement that specifies: The input data The input data The desired output The desired output The processing required to convert The processing required to convert Sometimes, the programmer receives a written specification from the systems analyst Other times, the programmer meets with users directly Other times, the programmer meets with users directly Return

6Copyright © 2003 by Prentice Hall Planning the Solution Algorithm – a detailed, step-by-step solution to the problem Several tools help plan the algorithm plan the algorithmplan the algorithm Desk-check the solution Carry out each step of the algorithm with pencil and paper Carry out each step of the algorithm with pencil and paper Return

7Copyright © 2003 by Prentice Hall Planning Tools Flowchart – a pictorial representation of the algorithm Flowchart – a pictorial representation of the algorithm Pseudocode – English-like language Pseudocode – English-like language Specifies algorithm with more precision than you can in English, but less than a programming language Return

8Copyright © 2003 by Prentice Hall Coding the Program Translating the algorithm from the planning stage into a formal programming language All languages have syntax rules Similar to grammatical rules Similar to grammatical rules The computer will reject a program with even a minor syntax error The computer will reject a program with even a minor syntax error Programs can be keyed into the computer by using a text editor Return

9Copyright © 2003 by Prentice Hall Testing the Program Two phases of testing the program Translation Translation Translation Converting the program you wrote into the binary instructions the CPU understands Converting the program you wrote into the binary instructions the CPU understands Debugging Debugging Identifying and correcting logic errors in the program Identifying and correcting logic errors in the program Return

10Copyright © 2003 by Prentice Hall Translation Compiler translates the program (source module) into a machine language version (object module) If the compiler detects syntax errors, it will produce messages describing those errors If the compiler detects syntax errors, it will produce messages describing those errors If no syntax errors exist, the object module will be linked to create a load module If no syntax errors exist, the object module will be linked to create a load module Load module is executed by the computer Load module is executed by the computer Return

11Copyright © 2003 by Prentice Hall Documenting the Program Materials are generated at each part of the process Common examples of documentation Flowchart and/or pseudocode Flowchart and/or pseudocode Comments within the source code Comments within the source code Testing procedures Testing procedures Layouts of input and output records Layouts of input and output records A narrative description of the program A narrative description of the program Return

12Copyright © 2003 by Prentice Hall Levels of Languages Lower-level languages – more like the 0s and 1s the computer itself uses Higher-level languages – more like the languages people use Divided into five generations

13Copyright © 2003 by Prentice Hall Five Generations of Languages Machine language Machine language Assembly languages Assembly languages High-level languages High-level languages Very high-level languages Very high-level languages Natural languages Natural languages

14Copyright © 2003 by Prentice Hall Machine Language Programs and memory locations are written in strings of 0s and 1s Problems with machine languages Programs are difficult to write and debug Programs are difficult to write and debug Each computer has its own machine language Each computer has its own machine language Only option available to early programmers Return

15Copyright © 2003 by Prentice Hall Assembly Languages Substitute mnemonic codes for 0s and 1s For example, A for add, C for compare, etc. For example, A for add, C for compare, etc. Use names rather than binary addresses for memory locations Use names rather than binary addresses for memory locations Require an assembler to translate the program into machine language Still used for programming chips and writing utility programs Return

16Copyright © 2003 by Prentice Hall High-Level Languages Transformed programming Programmers could focus on solving problems rather than manipulating hardware Programmers could focus on solving problems rather than manipulating hardware Programs could be written and debugged much more quickly Programs could be written and debugged much more quickly Requires a compiler to convert the statements into machine language Each computer has its own version of a compiler for each language Each computer has its own version of a compiler for each language Return

17Copyright © 2003 by Prentice Hall Very High-Level Languages Also called fourth-generation languages (4GLs) Considered nonprocedural languages The programmer specifies the desired results, and the language develops the solution The programmer specifies the desired results, and the language develops the solution Programmers can be about 10 times more productive using a fourth-generation language than a third-generation language Programmers can be about 10 times more productive using a fourth-generation language than a third-generation language Return

18Copyright © 2003 by Prentice Hall Natural Languages Resemble written or spoken English Programs can be written in a natural syntax, rather than in the syntax rules of a programming language Programs can be written in a natural syntax, rather than in the syntax rules of a programming language The language translates the instructions into code the computer can execute Return

19Copyright © 2003 by Prentice Hall Major Programming Languages FORTRAN COBOL BASIC RPG Visual Basic Visual Basic C Java

20Copyright © 2003 by Prentice Hall FORTRAN The first high-level language Stands for FORmula TRANslator Used primarily for engineering, mathematical, and scientific tasks Return

21Copyright © 2003 by Prentice Hall COBOL Stands for COmmon Business-Oriented Language Used primarily for business requirements Processes large data files Processes large data files Produces well-formatted reports Produces well-formatted reports Return

22Copyright © 2003 by Prentice Hall BASIC Stands for Beginners’ All- Purpose Symbolic Instruction Code Developed to teach programming to college students Became very popular with the introduction of the microcomputer Return

23Copyright © 2003 by Prentice Hall RPG Stands for Report Program Generator Designed to allow rapid creation of reports Programmer simply describes the source data and desired report format Programmer simply describes the source data and desired report format Return

24Copyright © 2003 by Prentice Hall Visual Basic Allows programmer to create Windows-like user interfaces Programmer drags a control (button, text box, etc.) onto the form Programmer drags a control (button, text box, etc.) onto the form VB creates the code associated with that control VB creates the code associated with that control VB is event-driven The user controls the program The user controls the program Return

25Copyright © 2003 by Prentice Hall C Originally designed to write systems software Offers the ease of use of a high-level language with the efficiency of an assembly language Offers the ease of use of a high-level language with the efficiency of an assembly language Very portable – can be used with virtually every combination of computer and operating system Return

26Copyright © 2003 by Prentice Hall Java A network-friendly programming language that permits a piece of software to run directly on many different platforms Allows programmers to write one version of the program, rather than a separate version of each platform Allows programmers to write one version of the program, rather than a separate version of each platform Very useful for Internet development Java applets can run in the user’s Web browser Java applets can run in the user’s Web browser Return

27Copyright © 2003 by Prentice Hall Object-Oriented Programming Object – a self-contained unit that contains both data and its related functions Key terms in object-oriented programming Encapsulation – an object isolates both its data and its related instructions Encapsulation – an object isolates both its data and its related instructions Attributes – facts that describe the object Attributes – facts that describe the object Also called properties Methods – instructions that tell the object to do something Methods – instructions that tell the object to do something Messages – an outside stimulus that results in the change of the state of an object Messages – an outside stimulus that results in the change of the state of an object

28Copyright © 2003 by Prentice Hall Using Objects Programmers define classes of objects The class contains all attributes that are unique to objects of that class The class contains all attributes that are unique to objects of that class An object is an instance (occurrence) of a class An object is an instance (occurrence) of a class Objects are arranged hierarchically in classes and subclasses Subclasses are derived from classes Subclasses are derived from classes Inheritance – a subclass possesses all attributes of the class from which it is derived Inheritance – a subclass possesses all attributes of the class from which it is derived Additional attributes can be coded in the subclasses Additional attributes can be coded in the subclasses

29Copyright © 2003 by Prentice Hall Activating the Object A message is sent to the object, telling it to do something The object’s methods tell it how to do it The object’s methods tell it how to do it Polymorphism – each object has its own way to process the message For example, the class may have a Move method, but each subclass implements that method differently For example, the class may have a Move method, but each subclass implements that method differently

30Copyright © 2003 by Prentice Hall Object-Oriented Languages C++ Java C# Visual Basic Visual Basic

31Copyright © 2003 by Prentice Hall C++ An enhancement of the C language Includes all features of C Includes all features of C Adds support for object-oriented programming Adds support for object-oriented programming Can be used as simply an improvement of C, without the object-oriented features Return

32Copyright © 2003 by Prentice Hall Java A pure object-oriented program Used to create small programs called applets Applets can be delivered over the Web and run on any platform Applets can be delivered over the Web and run on any platform Return

33Copyright © 2003 by Prentice Hall C# Microsoft’s answer to Java Has the same advantages over C++ that Java has Designed to work within Microsoft’s.NET environment.NET is designed for building, deploying, and running Web-based applications.NET is designed for building, deploying, and running Web-based applications Return

34Copyright © 2003 by Prentice Hall Visual Basic Previous versions supported some object technology The current version, VB.NET, is the first to support inheritance and polymorphism These two traits are required for a true object- oriented language These two traits are required for a true object- oriented language Return