Encyclopedia of Computer Science and Technology

388 programming languagesprogrammer could edit, compile, run, and debug programswithout leaving the main window.The release of Visual Basic by Microsoft a few yearslater brought a full graphical user interface (GUI). VisualBasic not only ran in Windows, it also gave programmersthe ability to design programs by arranging user interfaceelements (such as menus and dialog boxes) on the screenand then attaching code and setting properties to controlthe behavior of each interface object. This approach wassoon extended by Microsoft to development environmentsfor C and C++ (and later, Java) while Borland releasedDelphi, a visual Pascal development system. Today visualprogramming environments are available for most languages.Indeed, many programming environments canhost many different languages and target environments.Examples include Microsoft’s Visual Studio .NET and theopen-source Eclipse, which can be extended to new languagesvia plug-ins.Modern programming environments help the programmerin a number of ways. While the program is being written,the editor can highlight syntax errors as soon as they’remade. Whether arising during editing or after compilation,an error message can be clicked to bring up an explanation,and an extensive online help system can provide informationabout language keywords, built-in functions, datatypes, or other matters. The debugger lets the programmertrace the flow of execution or examine the value of variablesat various points in the program.Most large programs today actually consists of dozensor even hundreds of separate files, including header files,source code files for different modules, and resources suchas icons or graphics. The process of tracking the connections(or dependencies) between all these files, which usedto require a list called a makefile can now be handled automatically,and relationships between classes in object-orientedprograms can be shown visually.Researchers are working on a variety of imaginativeapproaches for future programming environments. Forexample, an interactive graphical display (see virtualreality) might be used to allow the programmer to ineffect walk through and interact with various representationsof the program.Further ReadingBurd, Barry. Eclipse for Dummies. Hoboken, N.J.: Wiley, 2004.Hladni, Ivan. Inside Delphi 2006. Plano, Tex.: Wordware Publishing,2006.Kernighan, Brian W., and Rob Pike. The UNIX Programming Environment.Englewood Cliffs, N.J.: Prentice Hall, 1984.Parsons, Andrew, and Nick Randolph. Professional Visual Studio2005. Indianapolis: Wiley, 2006.programming languagesThere are many ways to represent instructions to be carriedout by a computer. With early machines like ENIAC,programs consisted of a series of detailed machine instructions.The exact movement of data between the processor’sinternal storage (registers) and internal memory had to bespecified, along with the appropriate arithmetic operations.The evolution of a few major programming languages through fivedecades. There are actually hundreds of different programming languagesthat have seen at least some use in the past 50 years.This lowest level, least abstract form of programming languagesis hardest for humans to understand and use.The first step toward a more symbolic form of programmingis to use easy-to-remember names for instructions(such as ADD or CMP for “compare”) as well asto provide labels for storage locations (variables) andsubroutines (see procedures and functions). The fileof symbolic instructions (called source code) is read bya program called an assembler (see assembler), whichgenerates the low-level instructions and actual memoryaddresses to be used by the program. Because of its abilityto closely specify machine operations, assembly languageis still used for low-level hardware control or whenefficiency is at a premium.Most languages in use today are higher-level. Themainstream of programming languages consists of languagesthat are procedural in nature. That is, they specifya main set of instructions that are executed in sequence,although the program can branch off (see branchingstatements) or repeat a series of statements until a conditionis satisfied (see loop). A program can also calla set of instructions defined elsewhere in the program.Constant or variable data is declared to be of a certaintype such as integer or character (see data types) beforeit is used. There are also rules that determine what partsof a program can access what data (see variable). Forexamples of procedural languages, see Algol, BASIC, C,COBOL, FORTRAN, and Pascal.A variant of procedural languages is the object-orientedlanguage (see object-oriented programming). Such languages(see C++, Java, and Smalltalk) still use sequentialexecution and procedures, but the procedures are “packaged”together with relevant data into objects. In order todisplay a picture, for example, the program will call upona particular object (created from a class of such objects) toexecute its display function with certain parameters such aslocation and dimensions.