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ALGOL60 is one of the first imperative programming languages used for scientific calculations, which evolved from ALGOL58 and some elements of FORTRAN (dynamic arrays, call by value and name, local and global variables, scope, formal and actual parameters). Its initial name was the International Algebraic Language. Because ALGOL58 had a significant number of ambiguities and since its authors had so many new ideas, international conferences were organized in January 1960 in Paris, France and in April 1962 Rome, Italy to correct them. Those two conferences, especially the one in Paris, brought so many changes to the ALGOL language that today ALGOL58 very often is described only as a draft to ALGOL60. ALGOL60 is the product of thirteen representatives from seven countries, including John Backus co-author of the Backus-Naur Form, metalanguage used to define ALGOL and other programming languages. ALGOL60 was the first language not designed for a specific type of computer. It was also the first language that introduced structured programming. Despite the fact that ALGOL60 was a product of a group of European and American scientists, it was never as popular in the United States as it was in the Europe. One of the reasons was the lack of support from IBM, which was supporting its own products FORTRAN and PL/I. Another reason was that ALGOL60 was not designed to be a universal language, only scientific for algebraic calculations, as its original name indicates. As a result, ALGOL60 did not support operations on character strings, except string constants as parameters in procedure calls. However, only a procedure coded in a language other than ALGOL60 could use such a parameter. Also, input/output statements were not part of the language; they had to be implemented by external procedures. The next version of ALGOL, ALGOL68, eliminated many of its weaknesses. However, together with other improvements including parallel programming, structures,unions, new data types, bit patterns, complex numbers and others it made ALGOL language very complex and user unfriendly, which instead of increasing its popularity had an adverse effect. The significance of ALGOL60 in Europe lead to the creation of the library, called NUMAL, in the years 1973-1979 under direction of P.W. Hemker from the Mathematisch Centrum at Amsterdam and other mathematicians. NUMAL was updated and maintained until 1980 when it became apparent that interest in ALGOL60 was decreasing. ALGOL60 was a relatively small and simple language, which supported only four types of variables: various sizes of integers and real numbers, Boolean and switch, which have statement labels as values. The variable type is defined at the compile time. Since each variable has a specific type and the compiler checks that the arguments in each operation are the correct one, ALGOL60 is strongly typed. It also has a small number of basic constructs, which together with a small number of rules to combine those constructs make ALGOL60 strongly orthogonal. When we talk about elements of the structured programming in ALGOL60 we have to remember that ALGOL60 is implementing GOTO statements. One of the reasons structured programming was introduced was to minimize the use of the GOTO and avoid “spaghetti code”, which meant an unclear code. Some of the most important elements of the structured programming in ALGOL60 are begin-end block, which also enables nesting, recursion and procedures (parameters are passed either by name or by value). Other elements of structured programming, which also exist in ALGOL60 are if-then-else, for (with various stepping formats ad several stopping conditions), while and switch. Despite all the facts, ALGOL60’s greatest strength does not come from its computational abilities. It comes from its influence on most of the major programminglanguages invented in the future (e.g. Pascal, Basic, Simula67, Smalltalk80, C++, Java), due to the innovations introduced in programming (e.g. structured programming) and techniques used to design and define the language (e.g. Backus-Naur Form). No other language in the history of the programming has had so much influence like ALGOL60. EXAMPLE OF THE PROGRAM. //This program computes the average of the absolute value of an array using ALGOL60. begin integer N; Read Int(N); begin real array Data[1:N]; real sum, avg; integer i; sum:=0; for i:=1 step 1 until N do begin real val; Read Real(val); Data[i]:=if val<0 then -val else val end; for i:=1 step 1 until N do sum:=sum + Data[i]; avg:=sum/N; Print Real(avg) end end Bibliography: 1) W. Wesley Peterson “Introduction to Programming Languages”, Prentice-Hall Inc. 1974 2) Richard L. Wexelblat “History of Programming Languages”, Academic Press Inc. 1981 3) www.frostburg.edu/dept/cosc/htracy/cosc450/CHAPTERS/algol.htm#1%20HISTORY 4) http://cgibin.erols.com/ziring/cgi-bin/cep/cep.pl?_alpha=a 5) www.cwi.nl/~jankok/etc/Preamble.html 6)


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CUNY CISC 3160 - Lecture Notes

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