Computers: Tools for an Information Age Chapter 15 Programming and Languages: Telling the Computer What to Do

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

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

The Programming Process Five main steps Defining the problem Planning the solution Coding the program Testing the program Documenting the program

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

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

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

Coding the Program Translating the algorithm from the planning stage into a formal programming language All languages have syntax rules Similar to grammatical rules 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

Testing the Program Two phases of testing the program Translation Converting the program you wrote into the binary instructions the CPU understands Debugging Identifying and correcting logic errors in the program Return

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 no syntax errors exist, the object module will be linked to create a load module Load module is executed by the computer Return

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

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

Five Generations of Languages Machine language Assembly languages High-level languages Very high-level languages Natural languages

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 Each computer has its own machine language Only option available to early programmers Return

Assembly Languages Substitute mnemonic codes for 0s and 1s For example, A for add, C for compare, etc. 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

High-Level Languages Transformed programming Programmers could focus on solving problems rather than manipulating hardware 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 Return

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 Programmers can be about 10 times more productive using a fourth-generation language than a third-generation language Return

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 The language translates the instructions into code the computer can execute Return

Major Programming Languages FORTRAN COBOL BASIC RPG Visual Basic C Java

FORTRAN The first high-level language Stands for FORmula TRANslator Used primarily for engineering, mathematical, and scientific tasks Return

COBOL Stands for COmmon Business-Oriented Language Used primarily for business requirements Processes large data files Produces well-formatted reports Return

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

RPG Stands for Report Program Generator Designed to allow rapid creation of reports Programmer simply describes the source data and desired report format Return

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

C Originally designed to write systems software 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

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 Very useful for Internet development Java applets can run in the user’s Web browser Return

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 Attributes – facts that describe the object Also called properties Methods – instructions that tell the object to do something Messages – an outside stimulus that results in the change of the state of an object

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

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 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

Object-Oriented Languages Java C# Visual Basic

C++ An enhancement of the C language Includes all features of C Adds support for object-oriented programming Can be used as simply an improvement of C, without the object-oriented features Return

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 Return

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 Return

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 Return