Editing Computer program (section)

===Generations of programming language===
{{main|Programming language generations}}
[[File:W65C816S Machine Code Monitor.jpeg|thumb|[[Machine language]] monitor on a [[W65C816S]] [[microprocessor]]]]
The evolution of programming languages began when the [[EDSAC]] (1949) used the first [[Stored-program computer|stored computer program]] in its [[von Neumann architecture]].<ref name="sco-ch1-p17">{{cite book
  | last = Tanenbaum
  | first = Andrew S.
  | title = Structured Computer Organization, Third Edition
  | publisher = Prentice Hall
  | year = 1990
  | page = [https://archive.org/details/structuredcomput00tane/page/17 17]
  | isbn = 978-0-13-854662-5
  | url = https://archive.org/details/structuredcomput00tane/page/17
  }}</ref> Programming the EDSAC was in the first [[Programming language generations|generation of programming language]].<ref>{{Citation |last1=Wilkes |first1=M. V. |title=The EDSAC |date=1982 |work=The Origins of Digital Computers: Selected Papers |pages=417–421 |editor-last=Randell |editor-first=Brian |url=https://link.springer.com/chapter/10.1007/978-3-642-61812-3_34 |access-date=2025-04-25 |place=Berlin, Heidelberg |publisher=Springer |language=en |doi=10.1007/978-3-642-61812-3_34 |isbn=978-3-642-61812-3 |last2=Renwick |first2=W.|url-access=subscription }}</ref>

* The [[First-generation programming language|first generation of programming language]] is [[machine language]].<ref name="pis-ch4-p160">{{cite book
  | last = Stair
  | first = Ralph M.
  | title = Principles of Information Systems, Sixth Edition
  | publisher = Thomson
  | year = 2003
  | page = 160
  | isbn = 0-619-06489-7
}}</ref> ''Machine language'' requires the programmer to enter instructions using ''instruction numbers'' called [[machine code]]. For example, the ADD operation on the [[PDP-11]] has instruction number 24576.<ref name="sco-ch7-p399">{{cite book
  | last = Tanenbaum
  | first = Andrew S.
  | title = Structured Computer Organization, Third Edition
  | publisher = Prentice Hall
  | year = 1990
  | page = [https://archive.org/details/structuredcomput00tane/page/399 399]
  | isbn = 978-0-13-854662-5
  | url = https://archive.org/details/structuredcomput00tane/page/399
  }}</ref>

* The [[Second-generation programming language|second generation of programming language]] is [[assembly language]].<ref name="pis-ch4-p160"/> ''Assembly language'' allows the programmer to use [[Assembly language#Mnemonics|mnemonic]] [[Instruction_set_architecture#Instructions|instructions]] instead of remembering instruction numbers. An [[Assembler (computing)|assembler]] translates each assembly language mnemonic into its machine language number. For example, on the PDP-11, the operation 24576 can be referenced as ADD in the source code.<ref name="sco-ch7-p399"/> The four basic arithmetic operations have assembly instructions like ADD, SUB, MUL, and DIV.<ref name="sco-ch7-p399"/> Computers also have instructions like DW (Define [[Word (computer architecture)|Word]]) to reserve [[Random-access memory|memory]] cells. Then the MOV instruction can copy [[integer]]s between [[Processor register|registers]] and memory.

:* The basic structure of an assembly language statement is a label, [[Operation (mathematics)|operation]], [[operand]], and comment.<ref name="sco-ch7-p400">{{cite book
  | last = Tanenbaum
  | first = Andrew S.
  | title = Structured Computer Organization, Third Edition
  | publisher = Prentice Hall
  | year = 1990
  | page = [https://archive.org/details/structuredcomput00tane/page/400 400]
  | isbn = 978-0-13-854662-5
  | url = https://archive.org/details/structuredcomput00tane/page/400
  }}</ref>
::* ''Labels'' allow the programmer to work with [[Variable (computer science)|variable names]]. The assembler will later translate labels into physical [[memory address]]es.
::* ''Operations'' allow the programmer to work with mnemonics. The assembler will later translate mnemonics into instruction numbers.
::* ''Operands'' tell the assembler which data the operation will process.
::* ''Comments'' allow the programmer to articulate a narrative because the instructions alone are vague.
:: The key characteristic of an assembly language program is it forms a one-to-one mapping to its corresponding machine language target.<ref name="sco-ch7-p398">{{cite book
  | last = Tanenbaum
  | first = Andrew S.
  | title = Structured Computer Organization, Third Edition
  | publisher = Prentice Hall
  | year = 1990
  | page = [https://archive.org/details/structuredcomput00tane/page/398 398]
  | isbn = 978-0-13-854662-5
  | url = https://archive.org/details/structuredcomput00tane/page/398
  }}</ref>

* The [[Third-generation programming language|third generation of programming language]] uses [[compiler]]s and [[Interpreter (computing)|interpreters]] to execute computer programs. The distinguishing feature of a ''third generation'' language is its independence from particular hardware.<ref name="cpl_3rd-ch2-26">{{cite book
  | last = Wilson
  | first = Leslie B.
  | title = Comparative Programming Languages, Third Edition
  | publisher = Addison-Wesley
  | year = 2001
  | page = 26
  | isbn = 0-201-71012-9
}}</ref> Early languages include [[Fortran]] (1958), [[COBOL]] (1959), [[ALGOL]] (1960), and [[BASIC]] (1964).<ref name="pis-ch4-p160"/> In 1973, the [[C programming language]] emerged as a [[high-level language]] that produced efficient machine language instructions.<ref name="cpl_3rd-ch2-37">{{cite book
  | last = Wilson
  | first = Leslie B.
  | title = Comparative Programming Languages, Third Edition
  | publisher = Addison-Wesley
  | year = 2001
  | page = 37
  | isbn = 0-201-71012-9
}}</ref> Whereas ''third-generation'' languages historically generated many machine instructions for each statement,<ref name="pis-ch4-p160_quote1">{{cite book
  | last = Stair
  | first = Ralph M.
  | title = Principles of Information Systems, Sixth Edition
  | publisher = Thomson
  | year = 2003
  | page = 160
  | isbn = 0-619-06489-7
  | quote = With third-generation and higher-level programming languages, each statement in the language translates into several instructions in machine language.
}}</ref> C has statements that may generate a single machine instruction.{{efn|[[Operators in C and C++|Operators]] like <code>x++</code> will usually compile to a single instruction.}} Moreover, an [[optimizing compiler]] might overrule the programmer and produce fewer machine instructions than statements. Today, an entire [[programming paradigm|paradigm]] of languages fill the [[imperative programming|imperative]], ''third generation'' spectrum.

* The [[Fourth-generation programming language|fourth generation of programming language]] emphasizes what output results are desired, rather than how programming statements should be constructed.<ref name="pis-ch4-p160"/> [[Declarative language]]s attempt to limit [[Side effect (computer science)|side effects]] and allow programmers to write code with relatively few errors.<ref name="pis-ch4-p160"/> One popular ''fourth generation'' language is called [[Structured Query Language]] (SQL).<ref name="pis-ch4-p160"/> [[Database]] developers no longer need to process each database record one at a time. Also, a simple [[Select (SQL)|select statement]] can generate output records without having to understand how they are retrieved.