ALGOL 68 is an imperative computer programming language, conceived as a successor to the ALGOL 60 programming language, designed with the goal of a much wider scope of application and more rigorously defined syntax and semantics. The contributions of ALGOL 68 to the field of computer science have been deep, wide ranging and enduring, although many of these contributions were only publicly identified when they had reappeared in subsequently developed programming languages. ALGOL 68 features include expression-based syntax, user-declared types and structures/tagged-unions, a reference model of variables and reference parameters, string and matrix slicing, concurrency. ALGOL 68 was designed by the IFIP Working Group 2.1. On December 20, 1968, the language was formally adopted by Working Group 2.1 and subsequently approved for publication by the General Assembly of IFIP. ALGOL 68 was defined using a two-level grammar formalism invented by Adriaan van Wijngaarden. Van Wijngaarden grammars use a context-free grammar to generate an infinite set of productions that will recognize a particular ALGOL 68 program.
ALGOL 68 has been criticized, most prominently by some members of its design committee such as C. A. R. Hoare and Edsger Dijkstra, for abandoning the simplicity of ALGOL 60, becoming a vehicle for complex or overly general ideas, doing little to make the compiler writer's task easier, in contrast to deliberately simple contemporaries such as C, S-algol and Pascal. In 1970, ALGOL 68-R became the first working compiler for ALGOL 68. In the 1973 revision, certain features – such as proceduring and formal bounds – were omitted. C.f. The language of the unrevised report.r0 Though European defence agencies promoted the use of ALGOL 68 for its expected security advantages, the American side of the NATO alliance decided to develop a different project, the Ada programming language, making its use obligatory for US defense contracts. Algol 68 had a notable influence within the Soviet Union, details of which can be found in Andrey Ershov's 2014 paper: "ALGOL 68 and Its Impact on the USSR and Russian Programming" and "Алгол 68 и его влияние на программирование в СССР и России" - pages: 336 & 342.
Steve Bourne, on the Algol 68 revision committee, took some of its ideas to his Bourne shell and to C. The complete history of the project can be found in C. H. Lindsey's A History of ALGOL 68. For a full-length treatment of the language, see Programming Algol 68 Made Easy by Dr. Sian Mountbatten, or Learning Algol 68 Genie by Dr. Marcel van der Veer which includes the Revised Report. "A Shorter History of Algol 68" ALGOL 68 - 3rd generation ALGOL Mar. 1968: Draft Report on the Algorithmic Language ALGOL 68 - Edited by: A. van Wijngaarden, B. J. Mailloux, J. E. L. Peck and C. H. A. Koster. Oct. 1968: Penultimate Draft Report on the Algorithmic Language ALGOL 68 – Chapters 1-9 Chapters 10-12 – Edited by: A. van Wijngaarden, B. J. Mailloux, J. E. L. Peck and C. H. A. Koster. Dec. 1968: Report on the Algorithmic Language ALGOL 68 – Offprint from Numerische Mathematik, 14, 79-218. – Edited by: A. van Wijngaarden, B. J. Mailloux, J. E. L. Peck and C. H. A. Koster. WG 2.1 members active in the original design of ALGOL 68: Friedrich L. Bauer • Hans Bekic • Edsger Dijkstra※ • Fraser Duncan※ • Jan Garwick※ • Gerhard Goos • Tony Hoare※ • Peter Zilahy Ingerman • Kees Koster • Peter Landin • Charles Lindsey • Barry Mailloux • John McCarthy • Jack Merner • Peter Naur‡ • Manfred Paul • John Peck • Willem van der Poel • Brian Randell※ • Doug Ross • Klaus Samelson • Gerhard Seegmüller※ • Michel Sintzoff • Wlad Turski※ • Aad van Wijngaarden • Niklaus Wirth‡ • Mike Woodger※ • Nobuo Yoneda.
‡Resigned after. Sep. 1973: Revised Report on the Algorithmic Language Algol 68 - Springer-Verlag 1976 - Edited by: A. van Wijngaarden, B. J. Mailloux, J. E. L. Peck, C. H. A. Koster, M. Sintzoff, C. H. Lindsey, L. G. L. T. Meertens and R. G. Fisker. 1968: On December 20, 1968, the "Final Report" was adopted by the Working Group subsequently approved by the General Assembly of UNESCO's IFIP for publication. Translations of the standard were made for Russian, German and Bulgarian, later Japanese and Chinese; the standard was made available in Braille. 1984: TC97 considered Algol 68 for standardisation as "New Work Item" TC97/N1642. West Germany, Netherlands, USSR and Czechoslovakia willing to participate in preparing the standard but the USSR and Czechoslovakia "were not the right kinds of member of the right ISO committees" and Algol 68's ISO standardisation stalled. 1988: Subsequently ALGOL 68 became one of the GOST standards in Russia. GOST 27974-88 Programming language ALGOL 68 – Язык программирования АЛГОЛ 68 GOST 27975-88 Programming language ALGOL 68 extended – Язык программирования АЛГОЛ 68 расширенный There are about 60 such reserved words in the standard language: mode, op, proc, heap, long, short, bool, char, int, sema, void, file, struct, union, at "@", eitherr0, is ":=:", isnt is notr0 ":/=:" ":≠:", of "→"r0, false, nil "○", skip "~", co "¢", comment "¢", pr, case ~ in ~ ouse ~ in ~ out ~ esac "", for ~ from ~ to ~ by ~ while ~ do ~ o
Computer programming is the process of designing and building an executable computer program for accomplishing a specific computing task. Programming involves tasks such as: analysis, generating algorithms, profiling algorithms' accuracy and resource consumption, the implementation of algorithms in a chosen programming language; the source code of a program is written in one or more languages that are intelligible to programmers, rather than machine code, directly executed by the central processing unit. The purpose of programming is to find a sequence of instructions that will automate the performance of a task on a computer for solving a given problem; the process of programming thus requires expertise in several different subjects, including knowledge of the application domain, specialized algorithms, formal logic. Tasks accompanying and related to programming include: testing, source code maintenance, implementation of build systems, management of derived artifacts, such as the machine code of computer programs.
These might be considered part of the programming process, but the term software development is used for this larger process with the term programming, implementation, or coding reserved for the actual writing of code. Software engineering combines engineering techniques with software development practices. Reverse engineering is the opposite process. A hacker is any skilled computer expert that uses their technical knowledge to overcome a problem, but it can mean a security hacker in common language. Programmable devices have existed at least as far back as 1206 AD, when the automata of Al-Jazari were programmable, via pegs and cams, to play various rhythms and drum patterns. However, the first computer program is dated to 1843, when mathematician Ada Lovelace published an algorithm to calculate a sequence of Bernoulli numbers, intended to be carried out by Charles Babbage's Analytical Engine. Women would continue to dominate the field of computer programming until the mid 1960s. In the 1880s Herman Hollerith invented the concept of storing data in machine-readable form.
A control panel added to his 1906 Type I Tabulator allowed it to be programmed for different jobs, by the late 1940s, unit record equipment such as the IBM 602 and IBM 604, were programmed by control panels in a similar way. However, with the concept of the stored-program computers introduced in 1949, both programs and data were stored and manipulated in the same way in computer memory. Machine code was the language of early programs, written in the instruction set of the particular machine in binary notation. Assembly languages were soon developed that let the programmer specify instruction in a text format, with abbreviations for each operation code and meaningful names for specifying addresses. However, because an assembly language is little more than a different notation for a machine language, any two machines with different instruction sets have different assembly languages. Kathleen Booth created one of the first Assembly languages in 1950 for various computers at Birkbeck College. High-level languages allow the programmer to write programs in terms that are syntactically richer, more capable of abstracting the code, making it targetable to varying machine instruction sets via compilation declarations and heuristics.
The first compiler for a programming language was developed by Grace Hopper. When Hopper went to work on UNIVAC in 1949, she brought the idea of using compilers with her. Compilers harness the power of computers to make programming easier by allowing programmers to specify calculations by entering a formula using infix notation for example. FORTRAN, the first used high-level language to have a functional implementation which permitted the abstraction of reusable blocks of code, came out in 1957. In 1951 Frances E. Holberton developed the first sort-merge generator which ran on the UNIVAC I. Another woman working at UNIVAC, Adele Mildred Koss, developed a program, a precursor to report generators. In USSR, Kateryna Yushchenko developed the Address programming language for the MESM in 1955; the idea for the creation of COBOL started in 1959 when Mary K. Hawes, who worked for Burroughs Corporation, set up a meeting to discuss creating a common business language, she invited six people, including Grace Hopper.
Hopper was involved in developing COBOL as a business language and creating "self-documenting" programming. Hopper's contribution to COBOL was based on her programming language, called FLOW-MATIC. In 1961, Jean E. Sammet developed FORMAC and published Programming Languages: History and Fundamentals which went on to be a standard work on programming languages. Programs were still entered using punched cards or paper tape. See computer programming in the punch card era. By the late 1960s, data storage devices and computer terminals became inexpensive enough that programs could be created by typing directly into the computers. Frances Holberton created a code to allow keyboard inputs while she worked at UNIVAC. Text editors were developed that allowed changes and corrections to be made much more than with punched cards. Sister Mary Kenneth Keller worked on developing the programming language, BASIC when she was a graduate student at Dartmouth in the 1960s. One of the first object-oriented programming languages, was developed by seven programmers, including Adele Goldberg, in the 1970s.
In 1985, Radia Perlman developed the Spannin
String (computer science)
In computer programming, a string is traditionally a sequence of characters, either as a literal constant or as some kind of variable. The latter may allow its elements to be mutated and the length changed. A string is considered a data type and is implemented as an array data structure of bytes that stores a sequence of elements characters, using some character encoding. String may denote more general arrays or other sequence data types and structures. Depending on programming language and precise data type used, a variable declared to be a string may either cause storage in memory to be statically allocated for a predetermined maximum length or employ dynamic allocation to allow it to hold a variable number of elements; when a string appears in source code, it is known as a string literal or an anonymous string. In formal languages, which are used in mathematical logic and theoretical computer science, a string is a finite sequence of symbols that are chosen from a set called an alphabet. Let Σ be a non-empty finite set of symbols, called the alphabet.
No assumption is made about the nature of the symbols. A string over Σ is any finite sequence of symbols from Σ. For example, if Σ = 01011 is a string over Σ; the length of a string s can be any non-negative integer. The empty string is the unique string over Σ of length 0, is denoted ε or λ; the set of all strings over Σ of length n is denoted Σn. For example, if Σ = Σ2 =. Note that Σ0 = for any alphabet Σ; the set of all strings over Σ of any length is the Kleene closure of Σ and is denoted Σ*. In terms of Σn, Σ ∗ = ⋃ n ∈ N ∪ Σ n For example, if Σ = Σ* =. Although the set Σ* itself is countably infinite, each element of Σ* is a string of finite length. A set of strings over Σ is called a formal language over Σ. For example, if Σ =, the set of strings with an number of zeros, is a formal language over Σ. Concatenation is an important binary operation on Σ*. For any two strings s and t in Σ*, their concatenation is defined as the sequence of symbols in s followed by the sequence of characters in t, is denoted st.
For example, if Σ =, s = bear, t = hug st = bearhug and ts = hugbear. String concatenation is an non-commutative operation; the empty string ε serves as the identity element. Therefore, the set Σ* and the concatenation operation form a monoid, the free monoid generated by Σ. In addition, the length function defines a monoid homomorphism from Σ* to the non-negative integers. A string s is said to be a substring or factor of t if there exist strings u and v such that t = usv; the relation "is a substring of" defines a partial order on Σ*, the least element of, the empty string. A string s is said to be a prefix of t if there exists a string u such that t = su. If u is nonempty, s is said to be a proper prefix of t. Symmetrically, a string s is said to be a suffix of t if there exists a string u such that t = us. If u is nonempty, s is said to be a proper suffix of t. Suffixes and prefixes are substrings of t. Both the relations "is a prefix of" and "is a suffix of" are prefix orders. A string s = uv.
For example, if Σ = the string 0011001 is a rotation of 0100110, where u = 00110 and v = 01. The reverse of a string is a string in reverse order. For example, if s = abc the reverse of s is cba. A string, the reverse of itself is called a palindrome, which includes the empty string and all strings of length 1, it is useful to define an ordering on a set of strings. If the alphabet Σ has a total order one can define a total order on Σ* called lexicographical order. For example, if Σ = and 0 < 1 the lexicographical order on Σ* includes the relationships ε < 0 < 00 < 000 <... < 0001 < 001 < 01 < 010 < 011 < 0110 < 01111 < 1 < 10 < 100 < 101 < 111 < 1111 < 11111... The lexicographical order is total if the alphabetical order is, but isn't well-founded for any nontrivial alphabet if the alphabetical order is. See Shortlex for an alternative string ordering that preserves well-foundedness. A number of additional operations on strings occur in the formal theory; these are given in the article on string operations.
Strings admit the following interpretation as nodes on a graph: Fixed-length strings can be viewed as nodes on a hypercube Variable-length strings can be viewed as nodes on the k-ary tree, where k is the number of symbols in Σ Infinite strings can be viewed as i
In computer science, a for-loop is a control flow statement for specifying iteration, which allows code to be executed repeatedly. Various keywords are used to specify this statement: descendants of ALGOL use "for", while descendants of Fortran use "do". There are other possibilities, for example COBOL which uses "PERFORM VARYING". A for-loop has two parts: a header specifying the iteration, a body, executed once per iteration; the header declares an explicit loop counter or loop variable, which allows the body to know which iteration is being executed. For-loops are used when the number of iterations is known before entering the loop. For-loops can test a loop variable; the name for-loop comes from the English word for, used as the keyword in many programming languages to introduce a for-loop. The term in English dates to ALGOL 58 and was popularized in the influential ALGOL 60; the loop body is executed "for" the given values of the loop variable, though this is more explicit in the ALGOL version of the statement, in which a list of possible values and/or increments can be specified.
In FORTRAN and PL/I, the keyword DO is used for the same thing and it is called a do-loop. A for-loop statement is available in most imperative programming languages. Ignoring minor differences in syntax there are many differences in how these statements work and the level of expressiveness they support. For-loops fall into one of the following categories: The for-loop of languages like ALGOL, Simula, BASIC, Modula, Ada, Ocaml, F#, so on, requires a control variable with start- and end-values and looks something like this: Depending on the language, an explicit assignment sign may be used in place of the equal sign. An optional step-value may be included, although the exact syntaxes used for this differs a bit more between the languages; some languages require a separate declaration of the control variable, some do not. Another form was popularized by the C programming language, it requires 3 parts: the initialization, the condition, the afterthought and all these three parts are optional. The initialization declares.
The type of a variable should be same. The condition checks a condition, quits the loop if false; the afterthought is performed once every time the loop ends and repeats. Here is an example of the traditional for-loop in Java; these loops are sometimes called numeric for-loops when contrasted with foreach loops. This type of for-loop is a generalisation of the numeric range type of for-loop, as it allows for the enumeration of sets of items other than number sequences, it is characterized by the use of an implicit or explicit iterator, in which the loop variable takes on each of the values in a sequence or other data collection. A representative example in Python is: Where some_iterable_object is either a data collection that supports implicit iteration, or may in fact be an iterator itself; some languages have this in addition to another for-loop syntax. Some languages offer a for-loop that acts as if processing all iterations in parallel, such as the for all keyword in FORTRAN 95 which has the interpretation that all right-hand-side expressions are evaluated before any assignments are made, as distinct from the explicit iteration form.
For example, in the for statement in the following pseudocode fragment, when calculating the new value for A, except for the first the reference to A will obtain the new value, placed there in the previous step. In the for all version, each calculation refers only to the original, unaltered A. for i:= 2: N - 1 do A:= / 3. Some languages offer array assignment statements, that enable many for-loops to be omitted, thus pseudocode such as A:= 0. The example loop could be rendered as But whether that would be rendered in the style of the for-loop or the for all-loop or something else may not be described in the compiler manual. Introduced with ALGOL 68 and followed by PL/I, this allows the iteration of a loop to be compounded with a test, as in for i:= 1: N while A > 0 do etc. That is, a value is assigned to the loop variable i and only if the while expression is true will the loop body be executed. If the result were false the for-loop's execution stops short. Granted that the loop variable's value is defined after the termination of the loop the above statement will find the first non-positive element in array A, or, with suitable variations, the first non-blank character in a string, so on.
In computer programming a loop counter is the variable. It is so named because most uses of this construct result in the variable taking on a range of integer values in some orderly sequences (example. Starting at 0 and end at 10 in incre