Encyclopedia of Computer Science and Technology

algorithmbegan to seek a “universal” programming language thatwas not designed for a particular application or hardwareplatform. By 1957, the German GAMM (Gesellschaft fürangewandte Mathematik und Mechanik) and the AmericanACM (Association for Computing Machinery) had joinedforces to develop the specifications for such a language. Theresult became known as the Zurich Report or Algol-58, andit was refined into the first widespread implementation ofthe language, Algol-60.Language FeaturesAlgol is a block-structured, procedural language. Each variableis declared to belong to one of a small number of kindsof data including integer, real number (see data types),or a series of values of either type (see array). While thenumber of types is limited and there is no facility for definingnew types, the compiler’s type checking (making sure adata item matches the variable’s declared type) introduced alevel of security not found in most earlier languages.An Algol program can contain a number of separateprocedures or incorporate externally defined procedures(see library, program), and the variables with the samename in different procedure blocks do not interfere withone another. A procedure can call itself (see recursion).Standard control structures (see branching statementsand loop) were provided.The following simple Algol program stores the numbersfrom 1 to 10 in an array while adding them up, then printsthe total:begininteger array ints[1:10];integer counter, total;total := 0;for counter :=1 step 1 until counter > 10dobeginints [counter] := counter;total := total + ints[counter];end;printstring “The total is:”;printint (total);endAlgol’s LegacyThe revision that became known as Algol-68 expandedthe variety of data types (including the addition of boolean,or true/false values) and added user-defined typesand “structs” (records containing fields of different typesof data). Pointers (references to values) were also implemented,and flexibility was added to the parameters thatcould be passed to and from procedures.Although Algol was used as a production language insome computer centers (particularly in Europe), its relativecomplexity and unfamiliarity impeded its acceptance,as did the widespread corporate backing for the rival languagesFORTRAN and especially COBOL. Algol achievedits greatest success in two respects: for a time it becamethe language of choice for describing new algorithms forcomputer scientists, and its structural features would beadopted in the new procedural languages that emerged inthe 1970s (see Pascal and c).Further Reading“Algol 68 Home Page.” URL: http://www.algol68.org. AccessedApril 10, 2007.Backus, J. W., and others. “Revised Report on the Algorithmic LanguageAlgol 60.” Originally published in Numerische Mathematik,the Communications of the ACM, and the Journal of the BritishComputer Society. Available online. URL: http://www.masswerk.at/algol60/report.htm. Accessed April 10, 2007.algorithmWhen people think of computers, they usually think ofsilicon chips and circuit boards. Moving from relays tovacuum tubes to transistors to integrated circuits hasvastly increased the power and speed of computers, butthe essential idea behind the work computers do remainsthe algorithm. An algorithm is a reliable, definable procedurefor solving a problem. The idea of the algorithm goesback to the beginnings of mathematics and elementaryschool students are usually taught a variety of algorithms.For example, the procedure for long division by successivedivision, subtraction, and attaching the next digit isan algorithm. Since a bona fide algorithm is guaranteed towork given the specified type of data and the rote followingof a series of steps, the algorithmic approach is naturallysuited to mechanical computation.Algorithms in Computer ScienceJust as a cook learns both general techniques such as howto sauté or how to reduce a sauce and a repertoire of specificrecipes, a student of computer science learns both generalproblem-solving principles and the details of common algorithms.These include a variety of algorithms for organizingdata (see sorting and searching), for numeric problems(such as generating random numbers or finding primes),and for the manipulation of data structures (see list processingand queue).A working programmer faced with a new task first triesto think of familiar algorithms that might be applicable tothe current problem, perhaps with some adaptation. Forexample, since a variety of well-tested and well-understoodsorting algorithms have been developed, a programmer islikely to apply an existing algorithm to a sorting problemrather than attempt to come up with something entirelynew. Indeed, for most widely used programming languagesthere are packages of modules or procedures that implementcommonly needed data structures and algorithms (seelibrary, program).If a problem requires the development of a new algorithm,the designer will first attempt to determine whetherthe problem can, at least in theory, be solved (see computabilityand complexity). Some kinds of problems havebeen shown to have no guaranteed answer. If a new algorithmseems feasible, principles found to be effective in thepast will be employed, such as breaking complex problems