Encyclopedia of Computer Science and Technology

202 FORTRANearly days of microcomputing because the lack of need fora sophisticated interpreter or compiler meant that Forthsystems could run comfortably on systems that had perhaps16K or 64K of available RAM.Forth never caught on with the mainstream of programmers,however. Its very uniqueness and the unusual mindsetit required probably limited the number of people willing tolearn it. While Forth programs can be clearly organized,badly written Forth programs can be virtually impossibleto read. However, Forth is sometimes found “under thehood” in surprising places (for example, the PostScript pagedescription language is similar to Forth) and the languagestill has a considerable following in designing hardwarecontrol devices (see embedded systems).Further ReadingBrodie, L. Starting FORTH. 2nd ed. Upper Saddle River, N.J.: PrenticeHall, 1987.———. Thinking FORTH. 2nd ed. Upper Saddle River, N.J.: PrenticeHall, 1994.Forth Interest Group. Available online. URL: http://www.forth.org. Accessed August 14, 2007.Rather, Elizabeth D. Forth Application Techniques. Hawthorne,Calif.: FORTH, Inc., 2006.FORTRANAs computing became established throughout the 1950s,the need for a language that could express operations in amore “human-readable” language began to be acutely felt.In a high-level language, programmers define variables andwrite statements and expressions to manipulate them. Theprogrammer is no longer concerned with specifying thedetailed storage and retrieval of binary data in the computer,and is freed to think about program structure and theproper implementation of algorithms.Fortran (FORmula TRANslator) was the first widelyused high-level programming language. It was developedby a project begun in 1954 by a team under the leadershipof IBM researcher John Backus. The goal of the project wasto create a language that would allow mathematicians, scientists,and engineers to express calculations in somethingclose to the traditional notation. At the same time, a compilerwould have to be carefully designed so that it wouldproduce executable machine code that would be nearly asefficient as the code that would have been created throughthe more tedious process of using assembly languages. (Seecompiler and assembler.)The first version of the language, Fortran I, becameavailable as a compiler for IBM mainframes in 1957. Animproved (and further debugged version) soon followed.Fortran IV (1963) expanded the number of supporteddata types, added “common” data storage, and includedthe DATA statement, which made it easier to load literalnumeric values into variables. This mature version of Fortranwas widely embraced by scientists and engineers, whocreated immense libraries of code for dealing with calculationscommonly needed for their work.By the 1970s, the structured programming movementwas well under way. This school of programming emphasizeddividing programs into self-contained procedures intowhich data would be passed, processed, and returned. Theuse of unconditional branches (GOTO statements) as wascommon in Fortran was now discouraged. A new version ofthe language, Fortran 77 (or F77), incorporated many of thenew structural features. The next version, Fortran 90 (F90),added support for recursion, an important technique forcoding certain kinds of problems (see recursion). Mathematicslibraries were also modernized. FORTRAN 2003contains a number of new features, including support formodern programming structures (see object-orientedprogramming) and the ability to interface smoothly withprograms written in the C language. A relatively minor furtherrevision has the tentative name FORTRAN 2008.Sample ProgramThe following simple example illustrates some features of atraditional FORTRAN program:INTEGER INTARRAY(10)INTEGER ITEMS, COUNTER, SUM, AVGSUM = 0READ *, ITEMSDO 10 COUNTER = 1, ITEMSREAD *, INTARRAY(COUNTER)SUM = SUM + INTARRAY(COUNTER)10 CONTINUEAVG = SUM / ITEMSPRINT ‘SUM OF ITEMS IS: ’, SUMPRINT ‘AVERAGE IS: ’, AVGSTOPENDThe program creates an array holding up to ten integers(see array). The first number it reads is the number of itemsto be added up. It stores this in the variable ITEMS. A DOloop statement then repeats the following two statementsonce for each number from 1 to the total number of items.Each time the two statements are executed, COUNTER isincreased by 1. The statements read the next number fromthe array and add it to the running total in SUM. Finally, theaverage is calculated and the sum and average are printed.Like its contemporary, COBOL, Fortran is viewed bymany modern programmers as a rather clumsy and anachronisticlanguage (because of its use of line number references,for example). However, there is a tremendous legacyof tested, reliable Fortran code and powerful math libraries.(For example, a Fortran program can call library routinesto quickly get the sum or cross-product of any array ormatrix.) These features ensure that Fortran has continuingappeal and utility to users who are more concerned withgetting fast and accurate results than with the niceties ofprogramming style.Further ReadingChapman, Stephen J. Fortran 95/2003 for Scientists & Engineers.3rd ed. New York: McGraw-Hill, 2007.Chivers, Ian, and Jane Sleightholme. Introduction to Programmingwith Fortran: With Coverage of Fortran 90, 95, 2003 and 77.New York: Springer, 2005.