A computer program in its human-readable form is called source code. Source code needs another computer program to execute because computers can only execute their native machine instructions. Therefore, source code may be translated to machine instructions using a compiler written for the language. (Assembly language programs are translated using an .) The resulting file is called an . Alternatively, source code may execute within an written for the language.
If the source code is requested for execution, then the operating system loads the corresponding interpreter into memory and starts a process. The interpreter then loads the source code into memory to translate and execute each statement. Running the source code is slower than running an executable.6c Moreover, the interpreter must be installed on the computer.
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Rabbit hole
Where Computer program leads. Every connection below has a source: a link in this article, a shared Wikipedia category, or CirrusSearch text similarity. Articles already on your trail are left out.
The "Hello, World!" program is used to illustrate a language's basic syntax. The syntax of the language BASIC (1964) was intentionally limited to make the language easy to learn.7 For example, variables are not declared before being used.8 Also, variables are automatically initialized to zero.8 Here is an example computer program, in Basic, to average a list of numbers:9
10 INPUT "How many numbers to average?", A
20 FOR I = 1 TO A
30 INPUT "Enter number:", B
40 LET C = C + B
50 NEXT I
60 LET D = C/A
70 PRINT "The average is", D
80 END
Once the mechanics of basic computer programming are learned, more sophisticated and powerful languages are available to build large computer systems.10
In 1837, Jacquard's loom inspired Charles Babbage to attempt to build the Analytical Engine.11 The names of the components of the calculating device were borrowed from the textile industry. In the textile industry, yarn was brought from the store to be milled. The device had a store which consisted of memory to hold 1,000 numbers of 50 decimal digits each.12 Numbers from the store were transferred to the mill for processing. The engine was programmed using two sets of perforated cards. One set directed the operation and the other set inputted the variables.13 However, the thousands of cogged wheels and gears never fully worked together.14
Ada Lovelace worked for Charles Babbage to create a description of the Analytical Engine (1843).15 The description contained Note G which completely detailed a method for calculating Bernoulli numbers using the Analytical Engine. This note is recognized by some historians as the world's first computer program.14
Universal Turing machine
In 1936, Alan Turing introduced the Universal Turing machine, a theoretical device that can model every computation.16 It is a finite-state machine that has an infinitely long read/write tape. The machine can move the tape back and forth, changing its contents as it performs an algorithm. The machine starts in the initial state, goes through a sequence of steps, and halts when it encounters the halt state.17 All present-day computers are Turing complete.18
ENIAC
Glenn A. Beck changing a tube in ENIAC
The Electronic Numerical Integrator And Computer (ENIAC) was built between July 1943 and Fall 1945. It was a Turing complete, general-purpose computer that used 17,468 vacuum tubes to create the circuits. At its core, it was a series of Pascalines wired together.19 Its 40 units weighed 30 tons, occupied 1,800 square feet (167 m2), and consumed $650 per hour (in 1940s currency) in electricity when idle.19 It had 20 base-10accumulators. Programming the ENIAC took up to two months.19 Three function tables were on wheels and needed to be rolled to fixed function panels. Function tables were connected to function panels by plugging heavy black cables into plugboards. Each function table had 728 rotating knobs. Programming the ENIAC also involved setting some of the 3,000 switches. Debugging a program took a week.20 It ran from 1947 until 1955 at Aberdeen Proving Ground, calculating hydrogen bomb parameters, predicting weather patterns, and producing firing tables to aim artillery guns.21
Stored-program computers
Instead of plugging in cords and turning switches, a stored-program computer loads its instructions into memory just like it loads its data into memory.22 As a result, the computer could be programmed quickly and perform calculations at very fast speeds.23Presper Eckert and John Mauchly built the ENIAC. The two engineers introduced the stored-program concept in a three-page memo dated February 1944.24 Later, in September 1944, John von Neumann began working on the ENIAC project. On June 30, 1945, von Neumann published the First Draft of a Report on the EDVAC, which equated the structures of the computer with the structures of the human brain.23 The design became known as the von Neumann architecture. The architecture was simultaneously deployed in the constructions of the EDVAC and EDSAC computers in 1949.2526
IBM planned for each model to be programmed using PL/I.28 A committee was formed that included COBOL, FORTRAN and ALGOL programmers. The purpose was to develop a language that was comprehensive, easy to use, extendible, and would replace COBOL and FORTRAN.28 The result was a large and complex language that took a long time to compile.29
Switches for manual input on a Data General Nova 3, manufactured in the mid-1970s
Computers manufactured until the 1970s had front-panel switches for manual programming.30 The computer program was written on paper for reference. An instruction was represented by a configuration of on/off settings. After setting the configuration, an execute button was pressed. This process was then repeated. Computer programs also were automatically inputted via paper tape, punched cards or magnetic-tape. After the medium was loaded, the starting address was set via switches, and the execute button was pressed.30
Originally, integrated circuit chips had their function set during manufacturing. Chip makers designed custom chips for specific applications.35
In 1969, Busicom, a Japanese calculator company, contracted with Intel to manufacture 12 integrated circuit chips, each for a specific calculator function. Ted Hoff, the engineer tasked with the assignment, realized he could build one chip that could execute computer programs to perform the 12 calculator functions.36 The resulting chip was called the Intel 4004microprocessor.
IBM's System/360 (1964) CPU was not a microprocessor.
In 1978, the modern software development environment began when Intel upgraded the Intel 8080 to the Intel 8086. Intel simplified the Intel 8086 to manufacture the cheaper Intel 8088.38IBM embraced the Intel 8088 when they entered the personal computer market (1981). As consumerdemand for personal computers increased, so did Intel's microprocessor development. The succession of development is known as the x86 series. The x86 assembly language is a family of backward-compatiblemachine instructions. Machine instructions created in earlier microprocessors were retained throughout microprocessor upgrades. This enabled consumers to purchase new computers without having to purchase new application software. The major categories of instructions are:d
Programming language features exist to provide building blocks to be combined to express programming ideals.39 Ideally, a programming language should:39
express ideas directly in the code.
express independent ideas independently.
express relationships among ideas directly in the code.
combine ideas freely.
combine ideas only where combinations make sense.
express simple ideas simply.
The programming style of a programming language to provide these building blocks may be categorized into programming paradigms.40 For example, different paradigms may differentiate:40
Each of these programming styles has contributed to the synthesis of different .
Software engineering and computer programming
Prior to programming languages, Betty Jennings and Fran Bilas programmed the ENIAC by moving cables and setting switches.
Software engineering is a variety of techniques to produce qualitycomputer programs.116Computer programming is the process of writing or editing source code. In a formal environment, a systems analyst will gather information from managers about all the organization's processes to automate. This professional then prepares a detailed plan for the new or modified system.117 The plan is analogous to an architect's blueprint.117
Performance objectives
The systems analyst has the objective to deliver the right information to the right person at the right time. The critical factors to achieve this objective are:
Computer programs may be categorized along functional lines. The main functional categories are application software and system software. System software includes the operating system, which couples computer hardware with application software.132 The purpose of the operating system is to provide an environment where application software executes in a convenient and efficient manner.132 Both application software and system software execute utility programs. At the hardware level, a microcode program controls the circuits throughout the .
Notes
aThe Prolog language allows for a database of facts and rules to be entered in any order. However, a question about a database must be at the very end.
bEither the user or another program makes the request.
fWhereas this is a decimal number, PDP-11 code is always expressed as octal.
gOperators like x++ will usually compile to a single instruction.
hThe line numbers were typically incremented by 10 to leave room if additional statements were added later.
iThis function could be written more concisely as int increment_counter() { static int counter; return ++counter; } Static variables are automatically initialized to zero. ++counter is a prefix increment operator.
jThis is despite the metaphor of a stack, which normally grows from bottom to top.
kC also provides the function to allocate heap memory. It provides two additional services: 1) It allows the programmer to create an of arbitrary size. 2) It sets each to zero.
References
1"ISO/IEC 2382:2015". ISO. 2020-09-03. Archived from the original on 2016-06-17. Retrieved 2022-05-26. “[Software includes] all or part of the programs, procedures, rules, and associated documentation of an information processing system.”
2Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 7. ISBN 0-201-71012-9. “An alternative to compiling a source program is to use an interpreter. An interpreter can directly execute a source program[.]”
3Kerrisk, Michael (2010). The Linux Programming Interface. No Starch Press. p. 22. ISBN 978-1-59327-220-3. “The kernel can load a new program into memory[.]”
4Silberschatz, Abraham (1994). Operating System Concepts, Fourth Edition. Addison-Wesley. p. 98. ISBN 978-0-201-50480-4. “Informally, a process is a program in execution.”
A programming language is a set of keywords, symbols, identifiers, and rules by which programmers can communicate instructions to the computer.41 They follow a set of rules called a syntax.41
Programming languages get their basis from formal languages.42 The purpose of defining a solution in terms of its formal language is to generate an algorithm to solve the underlining problem.42 An algorithm is a sequence of simple instructions that solve a problem.43
The second generation of programming language is assembly language.48Assembly language allows the programmer to use mnemonicinstructions instead of remembering instruction numbers. An 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 R0,R0 in the source code.49 The four basic arithmetic operations have assembly instructions like ADD, SUB, MUL, and DIV.49 Assemblers also have instructions like DW (Define Word) to reserve memory cells. Then the MOV instruction can copy integers between registers and those memory cells.
The basic structure of an assembly language statement is a label, operation, operand, and comment.50
Labels allow the programmer to work with variable names. The assembler will later translate labels into physical memory addresses.
Operations allow the programmer to work with mnemonics.
Operands tell the assembler which data the operation will process. The assembler will later translate mnemonics and operands into instruction numbers.
Comments allow the programmer to articulate a narrative because the instructions alone may be opaque to humans.
The key characteristic of an assembly language program is it forms a one-to-one mapping to its corresponding machine language target.51
The third generation of programming language uses compilers and interpreters to execute computer programs. The distinguishing feature of a third generation language is its independence from particular hardware.52 Early languages include FORTRAN (1958), COBOL (1959), ALGOL (1960), and BASIC (1964).48 In 1973, the C programming language emerged as a high-level language that produced efficient machine language instructions.53 Whereas third-generation languages historically generated many machine instructions for each statement,54 C has statements that may generate a single machine instruction.g Moreover, an optimizing compiler might overrule the programmer and produce fewer machine instructions than statements. Today, an entire paradigm of languages fill the imperative, third generation spectrum.
The fourth generation of programming language emphasizes what output results are desired, rather than how programming statements should be constructed.48Declarative languages attempt to limit side effects and allow programmers to write code with relatively few errors.48 One popular fourth generation language is called Structured Query Language (SQL).48Database developers no longer need to process each database record one at a time. Also, a simple select statement can generate output records without having to understand how they are retrieved.
A declaration introduces a variable name to the computer program and assigns it to a datatype56 – for example: var x: integer;
An expression yields a value – for example: 2 + 2 yields 4
A statement might assign an expression to a variable or use the value of a variable to alter the program's control flow – for example: x := 2 + 2; if x = 4 then do_something();
Fortran
FORTRAN (1958) was unveiled as "The IBM Mathematical FORmula TRANslating system". It was designed for scientific calculations, without string handling facilities. Along with declarations, expressions, and statements, it supported:
However, non-IBM vendors also wrote Fortran compilers, but with a syntax that would likely fail IBM's compiler.57 The American National Standards Institute (ANSI) developed the first Fortran standard in 1966. In 1978, Fortran 77 became the standard until 1991. Fortran 90 supports:
COBOL (1959) stands for "COmmon Business Oriented Language". Fortran manipulated symbols. It was soon realized that symbols did not need to be numbers, so strings were introduced.58 The US Department of Defense influenced COBOL's development, with Grace Hopper being a major contributor. The statements were English-like and verbose. The goal was to design a language so managers could read the programs. However, the lack of structured statements hindered this goal.59
COBOL's development was tightly controlled, so dialects did not emerge to require ANSI standards. As a consequence, it was not changed for 15 years until 1974. The 1990s version did make consequential changes, like object-oriented programming.59
Algol
ALGOL (1960) stands for "ALGOrithmic Language". It had a profound influence on programming language design.60 Emerging from a committee of European and American programming language experts, it used standard mathematical notation and had a readable, structured design. Algol was first to define its syntax using the Backus–Naur form.60 This led to syntax-directed compilers. It added features like:
BASIC (1964) stands for "Beginner's All-Purpose Symbolic Instruction Code". It was developed at Dartmouth College for all of their students to learn.9 If a student did not go on to a more powerful language, the student would still remember Basic.9 A Basic interpreter was installed in the microcomputers manufactured in the late 1970s. As the microcomputer industry grew, so did the language.9
Statements could be programmed by preceding them with line numbers.h
The 'list' command displayed the program.
The 'run' command executed the program.
However, the Basic syntax was too simple for large programs.9 Recent dialects added structure and object-oriented extensions. Microsoft's Visual Basic is still widely used and produces a graphical user interface.8
C
C programming language (1973) got its name because the language BCPL was replaced with B, and AT&T Bell Labs called the next version "C". Its purpose was to write the UNIXoperating system.53 C is a relatively small language, making it easy to write compilers. Its growth mirrored the hardware growth in the 1980s.53 Its growth also was because it has the facilities of assembly language, but it uses a high-level syntax. It added advanced features like:
The global and static data region is located just above the program region. (The program region is technically called the text region. It is where machine instructions are stored.)
The global and static data region is technically two regions.61 One region is called the initialized data segment, where variables declared with default values are stored. The other region is called the block started by segment, where variables declared without default values are stored.
Variables stored in the global and static data region have their addresses set at compile time. They retain their values throughout the life of the process.
The global and static region stores the global variables that are declared on top of (outside) the main() function.62 Global variables are visible to main() and every other function in the source code.
On the other hand, variable declarations inside of main(), other functions, or within {}block delimiters are local variables. Local variables also include formal parameter variables. Parameter variables are enclosed within the parenthesis of a function definition.63 Parameters provide an interface to the function.
Local variables declared using the static prefix are also stored in the global and static data region.61 Unlike global variables, static variables are only visible within the function or block. Static variables always retain their value. An example usage would be the following function:i
int increment_counter() {
static int counter = 0;
counter++;
return counter;
}
The stack region is a contiguous block of memory located near the top memory address.64 Variables placed in the stack are populated from top to bottom.j64 A stack pointer is a special-purpose register that keeps track of the last memory address populated.64 Variables are placed into the stack via the assembly language PUSH instruction. Therefore, the addresses of these variables are set during runtime. The method for stack variables to lose their scope is via the POP instruction.
Local variables declared without the static prefix, including formal parameter variables,65 are called automatic variables62 and are stored in the stack.61 They are visible inside the function or block and lose their scope upon exiting the function or block.
The heap region is located below the stack.61 It is populated from the bottom to the top. The operating system manages the heap using a heap pointer and a list of allocated memory blocks.66 Like the stack, the addresses of heap variables are set during runtime. An out of memory error occurs when the heap pointer and the stack pointer meet.
C provides the malloc() library function to allocate heap memory.k67 Populating the heap with data is an additional copy function.l Variables stored in the heap are economically passed to functions using pointers. Without pointers, the entire block of data would have to be passed to the function via the stack.
C++
In the 1970s, software engineers needed language support to break large projects down into modules.68 One obvious feature was to decompose large projects physically into separate files. A less obvious feature was to decompose large projects logically into abstract datatypes.68 At the time, languages supported concrete (scalar) datatypes like integer numbers, floating-point numbers, and strings of characters. Abstract datatypes are structures of concrete datatypes, with a new name assigned. For example, a list of integers could be called IntegerList.
In object-oriented terminology, an abstract datatype is called a class. However, a class is only a definition; no memory is allocated. When memory is allocated to a class and bound to an identifier, it is called an object.69
C++ (1985) was originally called "C with Classes".70 It was designed to expand C's capabilities by adding the object-oriented facilities of the language Simula.71 A C++ classencapsulates related data items with the functions that manipulate them.72
C++ supports a syntax to model subset/superset relationships. In set theory, an element of a subset inherits all the attributes contained in the superset. For example, a student is a person. Therefore, the set of students is a subset of the set of persons. As a result, students inherit all the attributes common to all persons. Additionally, students have unique attributes that other people do not have. C++ models subset/superset relationships using inheritance.75
Namespaces
A C++ namespace provides context in case a name conflict occurs.76 Class names and function names may be duplicated in other source code files or third-party libraries. To wrap class names and function names in a namespace block, use the keyword namespace. The keyword is followed by an identifier, and the block is enclosed in parenthesis.
To instantiate a class or execute a function that is within a namespace, prepend the class or function name with the namespace name followed by a double colon. For example, foo::bar() denotes the function bar() residing in the namespace foo. Alternatively, execute the using directive followed by the namespace name. Then all the class and function names may be accessed without the double colon prefix.
A C++ module provides an improvement over the legacy #includepreprocessor directive.77 The #include directive allows for arbitrary files to be included in a C/C++ program. The goal is to have a common set of constants, datatypes, and function declarations across a large application.78
Modules are identified to the compiler by including the export module statement followed by the name of the module. Other source code files then import the same module name to perform the module's task.79
Class definitions and other named declarations must also be preceded with the export statement to be visible to other source code files. If a namespace is exported, then everything inside that namespace is also exported.80
Example
This is a module for the Gradeclass in an application modelling a school:
// Grade.cpp
// The "export module" statement allows other programs to "import" the named module 'wikipedia.examples.Grade'
export module wikipedia.examples.Grade;
// Declare the 'wikipedia::examples' namespace
namespace wikipedia::examples {
// Define the class "Grade"
// The "export" statement allows other modules to access this class
export class Grade {
private:
// The class variable "letter" is of type char
char letter;
public:
// Constructor
explicit Grade(char letter):
letter{letter} {}
// A member operation
char getLetter() const {
return letter;
}
};
}
A constructor function has the same name as the class name.81 It is executed when an object of a class is declared.82
This is a module for the Person class in an application modelling a school:
// Person.cpp
export module wikipedia.examples.Person;
// Import the standard library module 'std'
import std;
// Add the type 'std::string' into scope
using std::string;
namespace wikipedia::examples {
export class Person {
protected:
// The class variable "name" is a class type std::string
string name;
public:
explicit Person(const string& name):
name{name} {}
string getName() const {
return name;
}
};
}
This is a module for the Student class in an application modelling a school:
// Student.cpp
export module wikipedia.examples.Student;
import std;
import wikipedia.examples.Grade;
import wikipedia.examples.Person;
using std::string;
namespace wikipedia::examples {
// 'Student' is a subclass of 'Person'
export class Student : public Person {
private:
Grade grade;
public:
Student(const string& name, const Grade& grade):
Person(name), grade{grade} {}
Grade getGrade() const {
return grade;
}
};
}
The syntax public Person means that the Student class extends the Person class, inheriting all of its variables and methods (such as name and getName()).83
This is a driver program for demonstration:
// Main.cpp
import std;
import wikipedia.examples.Grade;
import wikipedia.examples.Student;
using wikipedia::examples::Grade;
using wikipedia::examples::Student;
int main() {
Student john("John Doe", Grade('A'));
std::println("Student name: {}, with grade {}", john.getName(), john.getGrade().getLetter());
}
Imperative languages have one major criticism: assigning an expression to a non-local variable may produce an unintended side effect.84Declarative languages generally omit the assignment statement and the control flow. They describe what computation should be performed and not how to compute it. Two broad categories of declarative languages are functional languages and logical languages.
The principle behind a functional language is to use lambda calculus as a guide for a well defined semantic.85 In mathematics, a function is a rule that maps elements from an expression to a range of values. Consider the function:
times_10(x) = 10 * x
The expression10 * x is mapped by the function times_10() to a range of values. One value happens to be 20. This occurs when x is 2. So, the application of the function is mathematically written as:
times_10(2) = 20
A functional language compiler will not store this value in a variable. Instead, it will push the value onto the computer's stack before setting the program counter back to the calling function. The calling function will then pop the value from the stack.86
Imperative languages do support functions. Therefore, functional programming can be achieved in an imperative language, if the programmer uses discipline. However, a functional language will force this discipline onto the programmer through its syntax. Functional languages have a syntax tailored to emphasize the what.87
A functional program is developed with a set of primitive functions followed by a single driver function.84 Consider the snippet:
int max(int a, int b) {
return a < b ? b : a;
}
int min(int a, int b) {
return a < b ? a : b;
}
int range(int a, int b, int c) {
return max(a, max(b, c)) - min(a, min(b, c));
}
The primitives are max() and min(). The driver function is range().
For example, printf("%d", range(10, 4, 7)); will print 6.
Lisp (1958) stands for "LISt Processor".90 It is tailored to process lists. A full structure of the data is formed by building lists of lists. In memory, a tree data structure is built. Internally, the tree structure lends nicely for recursive functions.91 The syntax to build a tree is to enclose the space-separated elements within parenthesis. The following is a list of three elements. The first two elements are themselves lists of two elements:
((A B) (HELLO WORLD) 94)
Lisp has functions to extract and reconstruct elements.92 The function head() returns a list containing the first element in the list. The function tail() returns a list containing everything but the first element. The function cons() returns a list that is the concatenation of other lists. Therefore, the following expression will return the list x:
cons(head(x), tail(x))
One drawback of Lisp is when many functions are nested, the parentheses may look confusing.87 Modern Lisp environments help ensure parenthesis match. As an aside, Lisp does support the imperative language operations of the assignment statement and goto loops.93 Also, Lisp is not concerned with the datatype of the elements at compile time.94 Instead, it assigns (and may reassign) the datatypes at runtime. Assigning the datatype at runtime is called dynamic binding.95 Whereas dynamic binding increases the language's flexibility, programming errors may linger until late in the software development process.95
Writing large, reliable, and readable Lisp programs requires forethought. If properly planned, the program may be much shorter than an equivalent imperative language program.87Lisp is widely used in artificial intelligence. However, its usage has been accepted only because it has imperative language operations, making unintended side-effects possible.89
ML
ML (1979) stands for "Meta Language". ML checks to make sure only data of the same type are compared with one another.96 For example, this function has one input parameter (an integer) and returns an integer:
fun times_10(n : int) : int = 10 * n;
ML is not parenthesis-eccentric like Lisp. The following is an application of times_10():
times_10 2
It returns "20 : int". (Both the results and the datatype are returned.)
Like Lisp, ML is tailored to process lists. Unlike Lisp, each element is the same datatype.97 Moreover, ML assigns the datatype of an element at compile time. Assigning the datatype at compile time is called static binding. Static binding increases reliability because the compiler checks the context of variables before they are used.98
The building blocks of a Prolog program are facts and rules. Here is a simple example:
cat(tom). % tom is a cat
mouse(jerry). % jerry is a mouse
animal(X) :- cat(X). % each cat is an animal
animal(X) :- mouse(X). % each mouse is an animal
big(X) :- cat(X). % each cat is big
small(X) :- mouse(X). % each mouse is small
eat(X,Y) :- mouse(X), cheese(Y). % each mouse eats each cheese
eat(X,Y) :- big(X), small(Y). % each big animal eats each small animal
After all the facts and rules are entered, then a question can be asked:
Will Tom eat Jerry?
?- eat(tom,jerry).
true
The following example shows how Prolog will convert a letter grade to its numeric value:
numeric_grade('A', 4).
numeric_grade('B', 3).
numeric_grade('C', 2).
numeric_grade('D', 1).
numeric_grade('F', 0).
numeric_grade(X, -1) :- not X = 'A', not X = 'B', not X = 'C', not X = 'D', not X = 'F'.
grade('The Student', 'A').
?- grade('The Student', X), numeric_grade(X, Y).
X = 'A',
Y = 4
Rule (2) is a recursive (inductive) definition. It can be understood declaratively, without the need to understand how it is executed.
Rule (3) shows how functions are represented by using relations. Here, the mother and father functions ensure that every individual has only one mother and only one father.
Prolog is an untyped language. Nonetheless, inheritance can be represented by using predicates. Rule (4) asserts that a creature is a superclass of a dragon.
Object-oriented programming is a programming method to execute operations (functions) on objects.101 The basic idea is to group the characteristics of a phenomenon into an object container and give the container a name. The operations on the phenomenon are also grouped into the container.101Object-oriented programming developed by combining the need for containers and the need for safe functional programming.102 This programming method need not be confined to an object-oriented language.103 In an object-oriented language, an object container is called a class. In a non-object-oriented language, a data structure (which is also known as a record) may become an object container. To turn a data structure into an object container, operations need to be written specifically for the structure. The resulting structure is called an abstract datatype.104 However, inheritance will be missing. Nonetheless, this shortcoming can be overcome.
This is a Cheader file for the Grade datatype in an application modelling a school:
The formal strategy to build object-oriented objects is to:105
Identify the objects. Most likely these will be nouns.
Identify each object's attributes. What helps to describe the object?
Identify each object's actions. Most likely these will be verbs.
Identify the relationships from object to object. Most likely these will be verbs.
For example:
A person is a human identified by a name.
A grade is an achievement identified by a letter.
A student is a person who earns a grade.
Syntax and semantics
Production rules consist of a set of terminals and non-terminals.
The syntax of a computer program is a list of production rules which form its grammar.106 A programming language's grammar correctly places its declarations, expressions, and statements.107 Complementing the syntax of a language are its semantics. The semantics describe the meanings attached to various syntactic constructs.108 A syntactic construct may need a semantic description because a production rule may have an invalid interpretation.109 Also, different languages might have the same syntax; however, their behaviors may be different.
The syntax of a language is formally described by listing the production rules. Whereas the syntax of a natural language is extremely complicated, a subset of the English language can have this production rule listing:110
a sentence is made up of a noun-phrase followed by a verb-phrase;
a noun-phrase is made up of an article followed by an adjective followed by a noun;
a verb-phrase is made up of a verb followed by a noun-phrase;
an article is 'the';
an adjective is 'big' or
an adjective is 'small';
a noun is 'cat' or
a noun is 'mouse';
a verb is 'eats';
The words in bold-face are known as non-terminals. The words in 'single quotes' are known as terminals.111
From this production rule listing, complete sentences may be formed using a series of replacements.112 The process is to replace non-terminals with either a valid non-terminal or a valid terminal. The replacement process repeats until only terminals remain. One valid sentence is:
sentence
noun-phraseverb-phrase
articleadjectivenounverb-phrase
theadjectivenounverb-phrase
thebignounverb-phrase
thebigcatverb-phrase
thebigcatverbnoun-phrase
thebigcateatsnoun-phrase
thebigcateatsarticleadjectivenoun
thebigcateatstheadjectivenoun
thebigcateatsthesmallnoun
thebigcateatsthesmallmouse
However, another combination results in an invalid sentence:
thesmallmouseeatsthebigcat
Therefore, a semantic is necessary to correctly describe the meaning of an eat activity.
One production rule listing method is called the Backus–Naur form (BNF).113 BNF describes the syntax of a language and itself has a syntax. This recursive definition is an example of a metalanguage.108 The syntax of BNF includes:
::= which translates to is made up of a[n] when a non-terminal is to its right. It translates to is when a terminal is to its right.
| which translates to or.
< and > which surround non-terminals.
Using BNF, a subset of the English language can have this production rule listing:
<sentence> ::= <noun-phrase><verb-phrase>
<noun-phrase> ::= <article><adjective><noun>
<verb-phrase> ::= <verb><noun-phrase>
<article> ::= the
<adjective> ::= big | small
<noun> ::= cat | mouse
<verb> ::= eats
Using BNF, a signed-integer has the production rule listing:114
The implementation phase is to program the best solution.
The maintenance phase lasts throughout the life of the system. Changes to the system after it is deployed may be necessary.123 Faults may exist, including specification faults, design faults, or coding faults. Improvements may be necessary. Adaption may be necessary to react to a changing environment.
Computer programmer
A computer programmer is a specialist responsible for writing or modifying the source code to implement the detailed plan.117 A programming team is likely to be needed because most systems are too large to be completed by a single programmer.124 However, adding programmers to a project may not shorten the completion time. Instead, it may lower the quality of the system.124 To be effective, program modules need to be defined and distributed to team members.124 Also, team members must interact with one another in a meaningful and effective way.124
Computer programmers may be programming in the small: programming within a single module.125 Chances are a module will execute modules located in other source code files. Therefore, computer programmers may be programming in the large: programming modules so they will effectively couple with each other.125 Programming-in-the-large includes contributing to the application programming interface (API).
Program modules
Modular programming is a technique to refine imperative language programs. Refined programs may reduce the software size, separate responsibilities, and thereby mitigate software aging. A program module is a sequence of statements that are bounded within a block and together identified by a name.126 Modules have a function, context, and logic:127
The function of a module is what it does.
The context of a module are the elements being performed upon.
The logic of a module is how it performs the function.
The module's name should be derived first by its function, then by its context. Its logic should not be part of the name.127 For example, function compute_square_root( x ) or function compute_square_root_integer( i : integer ) are appropriate module names. However, function compute_square_root_by_division( x ) is not.
The degree of interaction within a module is its level of cohesion.127Cohesion is a judgment of the relationship between a module's name and its function. The degree of interaction between modules is the level of coupling.128Coupling is a judgement of the relationship between a module's context and the elements being performed upon.
Coincidental Cohesion: A module has coincidental cohesion if it performs multiple functions, and the functions are completely unrelated. For example, function read_sales_record_print_next_line_convert_to_float(). Coincidental cohesion occurs in practice if management enforces silly rules. For example, "Every module will have between 35 and 50 executable statements."129
Logical Cohesion: A module has logical cohesion if it has available a series of functions, but only one of them is executed. For example, function perform_arithmetic( perform_addition, a, b ).
Temporal Cohesion: A module has temporal cohesion if it performs functions related to time. One example, function initialize_variables_and_open_files(). Another example, stage_one(), stage_two(), ...
Procedural Cohesion: A module has procedural cohesion if it performs multiple loosely related functions. For example, function read_part_number_update_employee_record().
Communicational Cohesion: A module has communicational cohesion if it performs multiple closely related functions. For example, function read_part_number_update_sales_record().
Informational Cohesion: A module has informational cohesion if it performs multiple functions, but each function has its own entry and exit points. Moreover, the functions share the same data structure. Object-oriented classes work at this level.
Functional Cohesion: a module has functional cohesion if it achieves a single goal working only on local variables. Moreover, it may be reusable in other contexts.
Content Coupling: A module has content coupling if it modifies a local variable of another function. COBOL used to do this with the alter verb.
Common Coupling: A module has common coupling if it modifies a global variable.
Control Coupling: A module has control coupling if another module can modify its control flow. For example, perform_arithmetic( perform_addition, a, b ). Instead, control should be on the makeup of the returned object.
Stamp Coupling: A module has stamp coupling if an element of a data structure passed as a parameter is modified. Object-oriented classes work at this level.
Data Coupling: A module has data coupling if all of its input parameters are needed and none of them are modified. Moreover, the result of the function is returned as a single object.
Data flow analysis
A sample function-level data-flow diagram
Data flow analysis is a design method used to achieve modules of functional cohesion and data coupling.130 The input to the method is a data-flow diagram. A data-flow diagram is a set of ovals representing modules. Each module's name is displayed inside its oval. Modules may be at the executable level or the function level.
The diagram also has arrows connecting modules to each other. Arrows pointing into modules represent a set of inputs. Each module should have only one arrow pointing out from it to represent its single output object. (Optionally, an additional exception arrow points out.) A daisy chain of ovals will convey an entire algorithm. The input modules should start the diagram. The input modules should connect to the transform modules. The transform modules should connect to the output modules.131
Enterprise applications may be developed in-house as a one-of-a-kind proprietary software.134 Alternatively, they may be purchased as off-the-shelf software. Purchased software may be modified to provide custom software. If the application is customized, then either the company's resources are used or the resources are outsourced. Outsourced software development may be from the original software vendor or a third-party developer.135
The potential advantages of in-house software are features and reports may be developed exactly to specification.136 Management may also be involved in the development process and offer a level of control.137 Management may decide to counteract a competitor's new initiative or implement a customer or vendor requirement.138 A merger or acquisition may necessitate enterprise software changes. The potential disadvantages of in-house software are time and resource costs may be extensive.134 Furthermore, risks concerning features and performance may be looming.
The potential advantages of off-the-shelf software are upfront costs are identifiable, the basic needs should be fulfilled, and its performance and reliability have a track record.134 The potential disadvantages of off-the-shelf software are it may have unnecessary features that confuse end users, it may lack features the enterprise needs, and the data flow may not match the enterprise's work processes.134
Application service provider
One approach to economically obtaining a customized enterprise application is through an application service provider.139 Specialty companies provide hardware, custom software, and end-user support. They may speed the development of new applications because they possess skilled information system staff. The biggest advantage is it frees in-house resources from staffing and managing complex computer projects.139 Many application service providers target small, fast-growing companies with limited information system resources.139 On the other hand, larger companies with major systems will likely have their technical infrastructure in place. One risk is having to trust an external organization with sensitive information. Another risk is having to trust the provider's infrastructure reliability.139
In the 1950s, the programmer, who was also the operator, would write a program and run it. After the program finished executing, the output may have been printed, or it may have been punched onto paper tape or cards for later processing.30 More often than not the program did not work. The programmer then looked at the console lights and fiddled with the console switches. If less fortunate, a memory printout was made for further study. In the 1960s, programmers reduced the amount of wasted time by automating the operator's job. A program called an operating system was kept in the computer at all times.140
When the kernel initially loads an executable into memory, it divides the address space logically into regions.143 The kernel maintains a master-region table and many per-process-region (pregion) tables—one for each running process.143 These tables constitute the virtual address space. The master-region table is used to determine where its contents are located in physical memory. The pregion tables allow each process to have its own program (text) pregion, data pregion, and stack pregion.
The program pregion stores machine instructions. Since machine instructions do not change, the program pregion may be shared by many processes of the same executable.143
To save time and memory, the kernel may load only blocks of execution instructions from the disk drive, not the entire execution file completely.142
The kernel is responsible for translating virtual addresses into physical addresses. The kernel may request data from the memory controller and, instead, receive a page fault.144 If so, the kernel accesses the memory management unit to populate the physical data region and translate the address.145
The kernel allocates memory from the heap upon request by a process.146 When the process is finished with the memory, the process may request for it to be freed.147 If the process exits without requesting all allocated memory to be freed, then the kernel performs garbage collection to free the memory.148
The kernel also ensures that a process only accesses its own memory, and not that of the kernel or other processes.142
The kernel program should perform file system management.142 The kernel has instructions to create, retrieve, update, and delete files.
The kernel program should perform device management.142 The kernel provides programs to standardize and simplify the interface to the mouse, keyboard, disk drives, printers, and other devices. Moreover, the kernel should arbitrate access to a device if two processes request it at the same time.
The kernel program should perform network management.149 The kernel transmits and receives packets on behalf of processes. One key service is to find an efficient route to the target system.
Programmers access files through a relatively simple interface that in turn executes a relatively complicated low-level I/O interface. The low-level interface includes file creation, file descriptors, file seeking, physical reading, and physical writing.
Programmers create processes through a relatively simple interface that in turn executes a relatively complicated low-level interface.
Programmers perform date/time arithmetic through a relatively simple interface that in turn executes a relatively complicated low-level time interface.151
The kernel program should provide a communication channel between executing processes.152 For a large software system, it may be desirable to engineer the system into smaller processes. Processes may communicate with one another by sending and receiving signals.
Originally, operating systems were programmed in assembly; however, modern operating systems are typically written in higher-level languages like C, Objective-C, and Swift.m
Utility program
A utility is a program that aids system administration and software execution. An operating system typically provides utilities to check hardware such as storage, memory, speakers, and printers.153 A utility may optimize the performance of a storage device. System utilities monitor hardware and network performance and may trigger an alert when a metric is outside the nominal range.154 A utility may compress files to reduce storage space and network transmission time.153 A utility may sort and merge data sets154 or detect computer viruses.154
Connecting two transistors in series forms the NAND gate.
Connecting two transistors in parallel forms the NOR gate.
Connecting a NOT gate to a NAND gate forms the AND gate.
Connecting a NOT gate to a NOR gate forms the OR gate.
These five gates form the building blocks of binary algebra—the digital logic functions of the computer.
Microcode instructions are mnemonics programmers may use to execute digital logic functions instead of forming them in binary algebra. They are stored in a CPU's control store.160 These hardware-level instructions move data throughout the data path.
The micro-instruction cycle begins when the microsequencer uses its microprogram counter to fetch the next machine instruction from random-access memory.161 The next step is to decode the machine instruction by selecting the proper output line to the hardware module.162 The final step is to execute the instruction using the hardware module's set of gates.
A symbolic representation of an ALU
Instructions to perform arithmetic are passed through an arithmetic logic unit (ALU).163 The ALU has circuits to perform elementary operations to add, shift, and compare integers. By combining and looping the elementary operations through the ALU, the CPU performs its complex arithmetic.
Microcode instructions move data between the CPU and the memory controller. Memory controller microcode instructions manipulate two registers. The memory address register is used to access each memory cell's address. The memory data register is used to set and read each cell's contents.164
lFor string variables, C provides the strdup() function. It executes both the allocation function and the copy function.
mThe UNIX operating system was written in C, macOS was written in Objective-C, and Swift replaced Objective-C.
nThe bottom-level interpreter is technically called the Level 1 layer. The Level 0 layer is the digital logic layer. Three middle layers exist, and the Level 5 layer is the Problem-oriented language layer.155
ISBN
978-0-13-854662-5
6Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 7. ISBN 0-201-71012-9.
7Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 30. ISBN 0-201-71012-9. “Their intention was to produce a language that was very simple for students to learn[.]”
8Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 31. ISBN 0-201-71012-9.
9Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 30. ISBN 0-201-71012-9.
10Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 30. ISBN 0-201-71012-9. “The idea was that students could be merely casual users or go on from Basic to more sophisticated and powerful languages[.]”
13McCartney, Scott (1999). ENIAC – The Triumphs and Tragedies of the World's First Computer. Walker and Company. p. 16. ISBN 978-0-8027-1348-3. “Babbage decided to make a calculating device driven by two sets of cards, one to direct the operation to be performed, and the other for the variables of the problem.”
15J. Fuegi; J. Francis (October–December 2003), "Lovelace & Babbage and the creation of the 1843 'notes'", Annals of the History of Computing, 25 (4): 16, 19, 25, Bibcode:2003IAHC...25d..16F, doi:10.1109/MAHC.2003.1253887
16Rosen, Kenneth H. (1991). Discrete Mathematics and Its Applications. McGraw-Hill, Inc. p. 654. ISBN 978-0-07-053744-6. “Turing machines can model all the computations that can be performed on a computing machine.”
17Linz, Peter (1990). An Introduction to Formal Languages and Automata. D. C. Heath and Company. p. 234. ISBN 978-0-669-17342-0.
18Linz, Peter (1990). An Introduction to Formal Languages and Automata. D. C. Heath and Company. p. 243. ISBN 978-0-669-17342-0. “[A]ll the common mathematical functions, no matter how complicated, are Turing-computable.”
26Huskey, Harry D. (2003-01-01), "EDVAC", Encyclopedia of Computer Science, GBR: John Wiley and Sons Ltd., pp. 626–628, ISBN 978-0-470-86412-8, retrieved 2025-04-25
35Faggin, Federico (2021). Silicon. Waterside Productions. p. 97. ISBN 978-1-949003-41-3. “In 1972, Vadasz abruptly told me he had hired someone to run Intel's custom chip business ...”
36Miller, Christopher (2022). Chip War. Simon & Schuster, LLC. p. 70. ISBN 978-1-9821-7200-8. “Hoff bet it would soon be cheaper to design a standardized logic chip that, coupled with a powerful memory chip [and] programmed with different types of software, could compute many different things.”
37"360 Revolution" (PDF). Father, Son & Co. 1990. Archived (PDF) from the original on 2022-10-10. Retrieved February 5, 2022.
39Stroustrup, Bjarne (2013). The C++ Programming Language, Fourth Edition. Addison-Wesley. p. 10. ISBN 978-0-321-56384-2.
40Stroustrup, Bjarne (2013). The C++ Programming Language, Fourth Edition. Addison-Wesley. p. 11. ISBN 978-0-321-56384-2.
41Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 159. ISBN 0-619-06489-7.
42Linz, Peter (1990). An Introduction to Formal Languages and Automata. D. C. Heath and Company. p. 2. ISBN 978-0-669-17342-0.
43Weiss, Mark Allen (1994). Data Structures and Algorithm Analysis in C++. Benjamin/Cummings Publishing Company, Inc. p. 29. ISBN 0-8053-5443-3.
44Dasgupta, Subrata (2014). It Began with Babbage -- The Genesis of Computer Science. Oxford University Press. ISBN 978-0-19-930941-2. “It [the EDSAC project] opened up an entirely new region of the stored-program computer paradigm, a new class of artifacts the likes of which had never been seen before: computer-programs or software.”
45Tanenbaum, Andrew S. (1990). Structured Computer Organization, Third Edition. Prentice Hall. p. 17. ISBN 978-0-13-854662-5. “His [John von Neumann] basic design, now known as a von Neumann machine, was used in the EDSAC, the first stored program computer, and is still the basis for nearly all digital computers, even now, almost half a century later. ... Each word held either two 20-bit instructions [a stored program] or a 39-bit signed integer.”
46Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 160. ISBN 0-619-06489-7. “The first generation of programming languages is machine language, which requires the use of binary symbols (0s and 1s).”
47Tanenbaum, Andrew S. (1990). Structured Computer Organization, Third Edition. Prentice Hall. p. 399. ISBN 978-0-13-854662-5. “Most people can remember that the abbreviations for add, subtract, multiply, and divide are ADD, SUB, MUL, and DIV, but few can remember that the machine instructions (for the PDP-11) are 24576, 57344, 28672, and 29184.”
48Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 160. ISBN 0-619-06489-7.
52Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 26. ISBN 0-201-71012-9.
53Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 37. ISBN 0-201-71012-9.
54Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 160. ISBN 0-619-06489-7. “With third-generation and higher-level programming languages, each statement in the language translates into several instructions in machine language.”
55Wilson, Leslie B. (1993). Comparative Programming Languages, Second Edition. Addison-Wesley. p. 75. ISBN 978-0-201-56885-1.
56Stroustrup, Bjarne (2013). The C++ Programming Language, Fourth Edition. Addison-Wesley. p. 40. ISBN 978-0-321-56384-2.
57Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 16. ISBN 0-201-71012-9.
58Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 24. ISBN 0-201-71012-9.
59Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 25. ISBN 0-201-71012-9.
60Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 19. ISBN 0-201-71012-9.
62Kernighan, Brian W.; Ritchie, Dennis M. (1988). The C Programming Language Second Edition. Prentice Hall. p. 31. ISBN 0-13-110362-8.
63Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 128. ISBN 0-201-71012-9.
64Kerrisk, Michael (2010). The Linux Programming Interface. No Starch Press. p. 121. ISBN 978-1-59327-220-3.
65Kerrisk, Michael (2010). The Linux Programming Interface. No Starch Press. p. 122. ISBN 978-1-59327-220-3.
66Kernighan, Brian W.; Ritchie, Dennis M. (1988). The C Programming Language Second Edition. Prentice Hall. p. 185. ISBN 0-13-110362-8.
67Kernighan, Brian W.; Ritchie, Dennis M. (1988). The C Programming Language Second Edition. Prentice Hall. p. 187. ISBN 0-13-110362-8.
68Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 38. ISBN 0-201-71012-9.
69Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 193. ISBN 0-201-71012-9.
70Stroustrup, Bjarne (2013). The C++ Programming Language, Fourth Edition. Addison-Wesley. p. 22. ISBN 978-0-321-56384-2.
71Stroustrup, Bjarne (2013). The C++ Programming Language, Fourth Edition. Addison-Wesley. p. 21. ISBN 978-0-321-56384-2.
72Hunter, David (1995). The Essentials of C++. Research & Education Association. p. 46. ISBN 0-87891-748-9. “Just as a structure definition encapsulates a set of related data items, a class definition encapsulates related data items and functions that manipulate them.”
73Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 39. ISBN 0-201-71012-9.
74Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 35. ISBN 0-201-71012-9.
75Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 192. ISBN 0-201-71012-9.
76Gregoire, Marc (2024). Professional C++ (6th ed.). John Wiley and Sons, Inc. p. 9. ISBN 9781394193172. “Namespaces address the problem of naming conflicts between different pieces of code.”
77Gregoire, Marc (2024). Professional C++ (6th ed.). John Wiley and Sons, Inc. p. 422. ISBN 9781394193172. “Header files do have a number of problems, though, such as avoiding multiple includes of the same header file and making sure header files are included in the correct order.”
78Gehani, Narain (1985). Advanced C: Food for the Educated Palate. Computer Science Press. p. 196. ISBN 0-88175-078-6.
79Gregoire, Marc (2024). Professional C++ (6th ed.). John Wiley and Sons, Inc. p. 5. ISBN 9781394193172. “If the program did not import that module, it would be unable to perform its only task of printing text.”
80Gregoire, Marc (2024). Professional C++ (6th ed.). John Wiley and Sons, Inc. p. 424. ISBN 9781394193172.
81Stroustrup, Bjarne (2013). The C++ Programming Language, Fourth Edition. Addison-Wesley. p. 49. ISBN 978-0-321-56384-2.
82Hunter, David (1999). The Essentials of C++. Research & Education Association. p. 46. ISBN 0-87891-748-9.
83Hunter, David (1999). The Essentials of C++. Research & Education Association. p. 65. ISBN 0-87891-748-9.
84Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 218. ISBN 0-201-71012-9.
85Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 217. ISBN 0-201-71012-9.
86Weiss, Mark Allen (1994). Data Structures and Algorithm Analysis in C++. Benjamin/Cummings Publishing Company, Inc. p. 103. ISBN 0-8053-5443-3. “When there is a function call, all the important information needs to be saved, such as register values (corresponding to variable names) and the return address (which can be obtained from the program counter)[.] ... When the function wants to return, it ... restores all the registers. It then makes the return jump. Clearly, all of this work can be done using a stack, and that is exactly what happens in virtually every programming language that implements recursion.”
87Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 230. ISBN 0-201-71012-9.
88Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 240. ISBN 0-201-71012-9.
89Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 241. ISBN 0-201-71012-9.
90Jones, Robin; Maynard, Clive; Stewart, Ian (December 6, 2012). The Art of Lisp Programming. Springer Science & Business Media. p. 2. ISBN 9781447117193.
91Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 220. ISBN 0-201-71012-9.
92Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 221. ISBN 0-201-71012-9.
93Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 229. ISBN 0-201-71012-9.
94Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 227. ISBN 0-201-71012-9.
95Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 222. ISBN 0-201-71012-9.
96Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 233. ISBN 0-201-71012-9.
97Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 235. ISBN 0-201-71012-9.
98Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 55. ISBN 0-201-71012-9.
100Kowalski, R., Dávila, J., Sartor, G. and Calejo, M., 2023. Logical English for law and education. In Prolog: The Next 50 Years (pp. 287–299). Cham: Springer Nature Switzerland.
101Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 35. ISBN 0-201-71012-9. “Simula was based on Algol 60 with one very important addition — the class concept. ... The basic idea was that the data (or data structure) and the operations performed on it belong together[.]”
102Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 39. ISBN 0-201-71012-9. “Originally, a large number of experimental languages were designed, many of which combined object-oriented and functional programming.”
103Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 284. ISBN 0-256-08515-3. “While it is true that OOD [(object oriented design)] as such is not supported by the majority of popular languages, a large subset of OOD can be used.”
104Weiss, Mark Allen (1994). Data Structures and Algorithm Analysis in C++. Benjamin/Cummings Publishing Company, Inc. p. 57. ISBN 0-8053-5443-3.
105Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 285. ISBN 0-256-08515-3.
106Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 290. ISBN 0-201-71012-9. “The syntax (or grammar) of a programming language describes the correct form in which programs may be written[.]”
107Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 78. ISBN 0-201-71012-9. “The main components of an imperative language are declarations, expressions, and statements.”
108Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 290. ISBN 0-201-71012-9.
109Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 294. ISBN 0-201-71012-9.
115Wilson, Leslie B. (2001). Comparative Programming Languages, Third Edition. Addison-Wesley. p. 297. ISBN 0-201-71012-9.
116Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. Preface. ISBN 0-256-08515-3.
117Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 507. ISBN 0-619-06489-7.
118Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 513. ISBN 0-619-06489-7.
119Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 514. ISBN 0-619-06489-7.
120Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 516. ISBN 0-619-06489-7.
121Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 8. ISBN 0-256-08515-3.
122Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 517. ISBN 0-619-06489-7.
123Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 345. ISBN 0-256-08515-3.
124Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 319. ISBN 0-256-08515-3.
125Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 331. ISBN 0-256-08515-3.
126Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 216. ISBN 0-256-08515-3.
127Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 219. ISBN 0-256-08515-3.
128Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 226. ISBN 0-256-08515-3.
129Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 220. ISBN 0-256-08515-3.
130Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 258. ISBN 0-256-08515-3.
131Schach, Stephen R. (1990). Software Engineering. Aksen Associates Incorporated Publishers. p. 259. ISBN 0-256-08515-3.
132Silberschatz, Abraham (1994). Operating System Concepts, Fourth Edition. Addison-Wesley. p. 1. ISBN 978-0-201-50480-4.
133Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 147. ISBN 0-619-06489-7. “The key to unlocking the potential of any computer system is application software.”
134Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 147. ISBN 0-619-06489-7.
135Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 147. ISBN 0-619-06489-7. “[A] third-party software firm, often called a value-added software vendor, may develop or modify a software program to meet the needs of a particular industry or company.”
136Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 148. ISBN 0-619-06489-7. “Heading: Proprietary Software; Subheading: Advantages; Quote: You can get exactly what you need in terms of features, reports, and so on.”
137Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 148. ISBN 0-619-06489-7. “Heading: Proprietary Software; Subheading: Advantages; Quote: Being involved in the development offers a further level of control over the results.”
138Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 147. ISBN 0-619-06489-7. “Heading: Proprietary Software; Subheading: Advantages; Quote: There is more flexibility in making modifications that may be required to counteract a new initiative by one of your competitors or to meet new supplier and/or customer requirements.”
139Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 149. ISBN 0-619-06489-7.
141Kerrisk, Michael (2010). The Linux Programming Interface. No Starch Press. p. 21. ISBN 978-1-59327-220-3.
142Kerrisk, Michael (2010). The Linux Programming Interface. No Starch Press. p. 22. ISBN 978-1-59327-220-3.
143Bach, Maurice J. (1986). The Design of the UNIX Operating System. Prentice-Hall, Inc. p. 152. ISBN 0-13-201799-7.
144Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 443. ISBN 978-0-13-291652-3.
145Lacamera, Daniele (2018). Embedded Systems Architecture. Packt. p. 8. ISBN 978-1-78883-250-2.
146Kernighan, Brian W.; Ritchie, Dennis M. (1988). The C Programming Language Second Edition. Prentice Hall. p. 185. ISBN 0-13-110362-8. “malloc calls upon the operating system to obtain more memory as needed.”
147Kernighan, Brian W.; Ritchie, Dennis M. (1988). The C Programming Language Second Edition. Prentice Hall. p. 185. ISBN 0-13-110362-8. “Thus its [the operating system's] free storage is kept as a list of free blocks.”
148Kerrisk, Michael (2010). The Linux Programming Interface. No Starch Press. p. 22. ISBN 978-1-59327-220-3. “Once a process has completed execution, the kernel ensures that the resources it uses are freed for subsequent reuse by later programs.”
149Kerrisk, Michael (2010). The Linux Programming Interface. No Starch Press. p. 23. ISBN 978-1-59327-220-3.
150Kernighan, Brian W. (1984). The Unix Programming Environment. Prentice Hall. p. 201. ISBN 0-13-937699-2.
151Kerrisk, Michael (2010). The Linux Programming Interface. No Starch Press. p. 187. ISBN 978-1-59327-220-3.
152Haviland, Keith (1987). Unix System Programming. Addison-Wesley Publishing Company. p. 121. ISBN 0-201-12919-1.
153Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 145. ISBN 0-619-06489-7.
154Stair, Ralph M. (2003). Principles of Information Systems, Sixth Edition. Thomson. p. 146. ISBN 0-619-06489-7.
155Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 5. ISBN 978-0-13-291652-3.
156Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 6. ISBN 978-0-13-291652-3.
157Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 243. ISBN 978-0-13-291652-3.
158Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 147. ISBN 978-0-13-291652-3.
159Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 148. ISBN 978-0-13-291652-3.
160Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 253. ISBN 978-0-13-291652-3.
161Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 255. ISBN 978-0-13-291652-3.
162Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 161. ISBN 978-0-13-291652-3.
163Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 166. ISBN 978-0-13-291652-3.
164Tanenbaum, Andrew S. (2013). Structured Computer Organization, Sixth Edition. Pearson. p. 249. ISBN 978-0-13-291652-3.
TimhowardrileyRestored useful information to the caption; computer terminals were relatively expensive for their time; terminals were still being purchased in the 1990s until the Gateway 2000 took over.+111diff
In computing, assembly language (alternatively assembler language or symbolic machine code), often referred to simply as assembly and commonly abbreviated as ASM or asm, is any low-level programming…
In mathematics, a sequence is a collection of objects possibly with repetition, that come in a specified order. Like a set, it contains members (also called elements, or terms).
A programming language is a formal language designed to express computations, typically supporting the specification of software both for humans and for computers.
Random-access memory (RAM;) is a form of electronic computer memory that can be read and changed in any order, typically used to store working data and machine code.
Software that translates code from one programming language to another
In computing, a compiler is software that translates computer code written in one programming language (the source language) into another language (the target language).
The Jacquard machine (French: [ʒakaʁ]) is a device fitted to a loom that simplifies the process of manufacturing textiles with such complex patterns as brocade, damask and matelassé.
Sequence of program instructions invokable by other software
In computer programming, a function (also procedure, method, subroutine, routine, or subprogram) is a callable unit of software logic that has a well-formed interface and behavior and can be invoked multiple times.
