A symbol is something such as an entity, picture, written word, sound, or particular mark that represents something else by association, resemblance, or convention.... that stands for a value
Value
Value may refer to:*Value , the non value of the perpindicular quantity of the quadratic function of the tenth value.*Value , the degree of importance, including the value independent on subjective valuations by any individual la la la... that may vary; the term usually occurs in opposition to constant, which is a symbol for a non-varying value, i.e. completely fixed or fixed in the context of use.
A spreadsheet is a computer application that simulates a paper worksheet. It displays multiple cells that together make up a grid consisting of rows and columns, each cell containing either alphanumeric text or numeric values.... , the variable lastname might stand for a customer's last name. The concepts of constants and variables are basic to all modern mathematics, science, engineering, and computer programming
Computer programming
Computer programming is the process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs. This source code is written in a programming language.... .
Actual change In some contexts of use, the varying of variables is literal: their values actually change.
In computer science, imperative programming is a programming paradigm that describes computation in terms of statement s that change a program state .... , variables are set and usually modified by the running program through explicit assignment
Assignment
'Assignment' may refer to:* Assignment , a type of modification to a variable* Assignment , a task given to students* Assignment , a transfer of rights between two parties... .
A symbol is something such as an entity, picture, written word, sound, or particular mark that represents something else by association, resemblance, or convention.... that stands for a value
Value
Value may refer to:*Value , the non value of the perpindicular quantity of the quadratic function of the tenth value.*Value , the degree of importance, including the value independent on subjective valuations by any individual la la la... that may vary; the term usually occurs in opposition to constant, which is a symbol for a non-varying value, i.e. completely fixed or fixed in the context of use.
A spreadsheet is a computer application that simulates a paper worksheet. It displays multiple cells that together make up a grid consisting of rows and columns, each cell containing either alphanumeric text or numeric values.... , the variable lastname might stand for a customer's last name. The concepts of constants and variables are basic to all modern mathematics, science, engineering, and computer programming
Computer programming
Computer programming is the process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs. This source code is written in a programming language.... .
What it means for a variable to vary
Actual change
In some contexts of use, the varying of variables is literal: their values actually change.
In computer science, imperative programming is a programming paradigm that describes computation in terms of statement s that change a program state .... , variables are set and usually modified by the running program through explicit assignment
Assignment
'Assignment' may refer to:* Assignment , a type of modification to a variable* Assignment , a task given to students* Assignment , a transfer of rights between two parties... . In a C
C (programming language)
C is a general-purpose computer programming language originally developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories to implement the Unix operating system.... program we can say:
int r = 5;
while (r*r < 100)
Dependence on other variables
Mathematics, the sciences, and non-imperative forms of programming such as pure functional programming or logical programming take a more abstract view: varying doesn't mean change, but rather, dependence on the values of other variables in the expression in which the variable occurs, or dependence of the value of the expression on that of the variable.
Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion .... E = m c2, E and m are variables, while c is a constant, the velocity of light in vacuo. This famous equation describes how the value E and m are related, but that c is fixed.
The ideal gas law is the equation of state of a hypothetical ideal gas, first stated by Beno?t Paul ?mile Clapeyron in 1834. The law is derived from the fact that in the ideal state of any gas a given number of its "particles" occupy the same volume, and that volume changes are inverse to pressure changes and linear to temperature changes.... , PV = nRT describes the relationship between volume V, pressure P and temperature T; here, n is a constant, but a chemist will try to juggle one or more of the variables to fit the others, knowing full they can't beat the law.
Mathematics is the study of quantity, structure, space, change, and related topics of pattern and form. Mathematicians seek out patterns whether found in numbers, space, natural science, computers, imaginary abstractions, or elsewhere.... , in the theory of polynomials, a second-order polynomial is generally denoted as a x2 + b x + c, where a, b and c are called constant term
Constant term
In mathematics, the constant term of a polynomial is the term of degree 0. For example, in the polynomialover the variable X, the constant term is 3.... s while x is called a variable, as what is usually being studied is how the value of the function varies with x, for given values of a, b and c.
Notation for variables
In mathematics, single-symbol names for variables are the norm, with x, y, z, and t being most common; constants are usually denoted as a, b, c.
In written mathematics
Mathematics
Mathematics is the study of quantity, structure, space, change, and related topics of pattern and form. Mathematicians seek out patterns whether found in numbers, space, natural science, computers, imaginary abstractions, or elsewhere.... , variables and constants are usually set in an italic
Italic
Italic means "of or from Italy". The term is most commonly used to refer to the people and languages of what is now Italy from the historic period before the Roman Empire.... typeface.
Specific branches and applications of mathematics usually have specific naming convention
Naming convention
A naming convention is a convention for naming things. The intent is to allow useful information to be deduced from the names based on regularities.... s for variables. Variables with similar roles or meanings are often assigned consecutive letters. For example, the three axes in 3D coordinate space
Coordinate space
In mathematics, specifically in linear algebra, the coordinate space, Fn, is the prototypical example of an n-dimensional vector space over a field F.... are conventionally called x, y, and z, while random variables in statistics are usually named X, Y, Z. In physics, the names of variables are largely determined by the physical quantity
Physical quantity
A physical quantity is a physical property that can be Quantitative. This means it can be measured and/or calculated and expressed in numbers. For example, "weight" is a physical quantity that can be expressed by stating a number of some basic measurement unit such as pound or kilograms, while "beauty" is a property that is difficult to desc... they describe, but various naming conventions exist.
Statistics is a Mathematics pertaining to the collection, analysis, interpretation or explanation, and presentation of data. It also provides tools for prediction and forecasting based on data.... is to use X, Y, Z for the names of random variables, with these being replaced by x, y, z for observations or sample outcomes of those random variabes. Another convention sometimes used in statistics is to denote population values of particular statistics by lower (or upper) case greek letters, with sample-based estimates of those quantities being denoted by the corresponding lower (or upper) case letters from the ordinary alphabet.
Computer programming is the process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs. This source code is written in a programming language.... and other computer applications, variables and constants commonly take multiple-character names, e.g. COST or total. Single-character names are most commonly used for auxiliary variables; typically, i, j, k for integer variables, and x, y, z for real-valued ones.
History
Much of the basic theory for which we use variables today, such as school geometry
Geometry
Geometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers.... and algebra
Algebra
Algebra is a branch of mathematics concerning the study of structure , relation , and quantity. Together with geometry, mathematical analysis, combinatorics, and number theory, algebra is one of the main branches of mathematics.... , was developed thousands of years ago, but the use of symbolic formulae and variables is only several hundreds of years old. Arabic algebra texts such as the Al-Jabr
The Compendious Book on Calculation by Completion and Balancing
, also known under a shorter name spelled as 'Hisab al-jabr w?al-muqabala', ' Kitab al-Jabr wa-l-Muqabala' and other transliterations) is a mathematical book written in Arabic, in approximately 820 AD by the Islamic mathematics, Muhammad ibn Musa al-Khwarizmi.... still described mathematics in full text rather than symbolic formulae, but denoted the variable quantity in Arabic
Arabic language
Arabic is a Central Semitic language, thus related to and classified alongside other Semitic languages languages such as Hebrew language and Aramaic language.... word šay' ????? = “thing”;. This was taken into Old Spanish
Old Spanish language
Old Spanish, or Old Castilian, is an early form of the Spanish language that was spoken from 10th Century until 15th Century, before the consonantic readjustment occurred and evolution into Spanish language.... with the pronunciation “šei”, which was written xei, and was soon habitually abbreviated to ; and this is still the customary variable name in many fields today. It started the habit of using letters to represent variables in algebra
Algebra
Algebra is a branch of mathematics concerning the study of structure , relation , and quantity. Together with geometry, mathematical analysis, combinatorics, and number theory, algebra is one of the main branches of mathematics.... . Beyond mathematics, “X” has come to represent a generic placeholder variable whose value is unknown or secret, as in project X or mister X.
A open sentence is described as "open" in the sense that its truth value is meaningless until its variables are replaced with specific numbers, at which point the truth value can usually be determined .... s. For instance, in the formula x + 1 = 5, x
X (disambiguation)
X is the twenty-fourth letter of the Latin alphabet.X may also refer to:... is a variable which represents an "unknown" number
Number
A number is a mathematical object used in counting and measurement. A notational symbol which represents a number is called a Numeral system, but in common usage the word number is used for both the abstract object and the symbol, as well as for the numeral for the number.... . Variables are often represented by letter
Letter (alphabet)
A letter is an element in an alphabetic system of writing, such as the Greek alphabet and its descendants. Each letter in the written language is usually associated with one phoneme in the spoken form of the language.... s of the Roman alphabet, or those of other alphabet
Alphabet
An alphabet is a standardized set of letter basic written symbols each of which roughly represents a phoneme, a spoken language, either as it exists now or as it was in the past.... s, such as Greek
Greek alphabet
The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE.... , and use other special symbols.
In mathematics, variables are essential because they let quantitative relationships to be stated in a general way. If we were forced to use actual values, then the relationships would only apply in a more narrow set of situations.For example:
State a mathematical definition for finding the number twice that of ANY other finite number:
double(x) = x + x.
Now, all we need to do to find the double of a number is replace x with any number we want.
double(1) = 1 + 1 = 2
double(3) = 3 + 3 = 6
double(55) = 55 + 55 = 110
etc.
So in this example, the variable x is a "placeholder" for any number— that is to say, a variable. One important thing we assume is that the value of x does not change, even though we don't know what x is. But in some algorithms, obviously, will change x, and there are various ways to then denote if we mean its old or new value— again, generally not knowing either, but perhaps (for example) that one is less than the other.
Name conventions
Mathematics has many conventions. Below are some of the more common. Many of the symbols have other conventional uses, but they may actually represent a constant or a specific function rather than a variable.
In mathematics, a sequence is an ordered list of objects . Like a Set , it contains Element , and the number of terms is called the length of the sequence.... .
a, b, c, and d (sometimes extended to e and f) usually play similar roles or are made to represent parallel notions in a mathematical context. They often represent constants.
The coefficients in an equation, for example the general expression of a polynomial
Polynomial
In mathematics, a polynomial is an expression constructed from variables and constants, using the operations of addition, subtraction, multiplication, and constant non-negative whole number exponents.... or a Diophantine equation
Diophantine equation
In mathematics, a Diophantine equation is an indeterminate equation polynomial equation that allows the variables to be integers only. Diophantine problems have fewer equations than unknown variables and involve finding integers that work correctly for all equations.... are often a, b, c, d, e, and f.
Function may refer to:* Function , explaining why a feature survived selection* Function , an abstract entity that associates an input to a corresponding output according to some rule... s.
i, j, and k are often used as subscripts or index variables.
l and w are often used to represent the length and width of a figure.
The integers are natural numbers including 0 and their negative and non-negative numberss . They are numbers that can be written without a fractional or decimal component, and fall within the set .... s and usually play similar roles or are made to represent parallel notions in a mathematical context.
n typically denotes a count of objects, or, in statistics, the number of individuals.
In mathematics, a prime number is a natural number which has exactly two distinct natural number divisors: 1 and itself. An infinitude of prime numbers exists, as demonstrated by Euclid around 300 BC.... s, or relatively prime numbers.
p, q, and r usually play similar roles or are made to represent parallel notions in a mathematical context.
r often denotes a remainder or modulus.
r, s, and t usually play similar roles or are made to represent parallel notions in a mathematical context.
u and v usually play similar roles or are made to represent parallel notions in a mathematical context, such as denoting a vertex (graph theory)
Vertex (graph theory)
In graph theory, a vertex or node is the fundamental unit out of which graphs are formed: an undirected graph consists of a set of vertices and a set of edges , while a directed graph consists of a set of vertices and a set of arcs .... .
w, x, y, and z usually play similar roles or are made to represent parallel notions in a mathematical context, such as representing unknowns in an equation.
x, y and z correspond to the three Cartesian axes. In many two-dimensional cases, y will be expressed in terms of x; if a third dimension is added, z is expressed in terms of x and y.
In geometry and trigonometry, an angle is the figure formed by two Ray sharing a common endpoint, called the vertex of the angle . The magnitude of the angle is the "amount of rotation" that separates the two rays, and can be measured by considering the length of circular arc swept out when one ray is rotated about the vertex to coincide... measures.
usually represents an arbitrarily small positive number.
In statistics, standard deviation is a simple measure of the variability or statistical dispersion of a data set. A low standard deviation indicates that all of the data points are very close to the same value , while high standard deviation indicates that the data are ?spread out? over a large range of values.... in a statistical context.
Statistics is a Mathematics pertaining to the collection, analysis, interpretation or explanation, and presentation of data. It also provides tools for prediction and forecasting based on data.... , variables refer to measurable attributes, as these typically vary over time or between individuals. Variables can be discrete
Discrete probability distribution
Discrete probability distributions arise in the mathematical description of probability theory and statistical analysis in which the values that might be observed are restricted to being within a pre-defined list of possible values.... (taking values from a finite or countable set), continuous
Continuous probability distribution
In probability theory, a probability distribution is called continuous if its cumulative distribution function is continuous function. This is equivalent to saying that for random variables X with the distribution in question, Pr[X = a] = 0 for all real numbers a, i.e.: the probability that X attains the value a is zer... (having a continuous
Continuous function
In mathematics, a continuous function is a function for which, intuitively, small changes in the input result in small changes in the output. Otherwise, a function is said to be discontinuous.... distribution function
Cumulative distribution function
In probability theory and statistics, the cumulative distribution function or just distribution function, completely describes the probability distribution of a real-valued random variable X.... ), or neither. Temperature is a continuous variable, while the number of legs of an animal is a discrete variable. This concept of a variable is widely used in the natural
Natural science
In science, the term natural science refers to a methodological naturalism approach to the study of the universe, which is understood as obeying rules or law of nature origin.... , medical and social sciences.
The terms "dependent variable" and "independent variable" are used in similar but subtly different ways in mathematics and statistics as part of the standard terminology in those subjects.... s" and "dependent variables", the latter being expected to vary in value in response to changes in the former. In other words, an independent variable is presumed to potentially affect a dependent one. In experiments, independent variables include factors that can be altered or chosen by the researcher independent of other factors.
So, in an experiment to test if the boiling point of water changes with altitude, the altitude is under direct control and is the independent variable, and the boiling point is presumed to depend upon it, so being the dependent variable. The results of an experiment, or information to be used to draw conclusions, are known as data
DATA
Debt, AIDS, Trade in Africa is a multinational Non-governmental organization founded in January 2002 in London by U2's Bono along with Robert Sargent Shriver III and activists from the Jubilee 2000 Drop the Debt campaign.... . It is often important to consider which variables to allow, or directly control or eliminate, in the design of experiments
Design of experiments
Design of experiments, or experimental design, is the design of all information-gathering exercises where variation is present, whether under the full control of the experimenter or not.... .
There are also quasi-independent variables, which are used by researchers to group things without affecting the variable itself. For example, to separate people into groups by their sex does not change whether they are male of female. Or a researcher may separate people, arbitrarily, on the amount of coffee they had drunk before beginning an experiment. The researcher cannot change the past, but can use it to split people into groups.
While independent variables can refer to quantities and qualities that are under experimental control, they can also include extraneous factors that influence results in a confusing or undesired manner. In statistics the techique to work this out is called correlation
Correlation
In probability theory and statistics, correlation indicates the strength and direction of a linear relationship between two random variables.... .
If strongly confounding variables exist that can substantially change the result, it makes it harder to interpret. For example, a study on cancer against age will also have to take into account variables such as income, location
Location (geography)
In geography, location is a position or point in physical space that something occupies on Earths' surface. An reality location can often be designated using a specific pairing of latitude and longitude, a Cartesian coordinate system grid , a Spherical coordinate system, or an ellipsoid-based system .... , stress
Stress (medicine)
Stress is a biological term which refers to the consequences of the failure of a human or animal body to respond appropriately to emotional or body threats to the organism, whether actual or imagined.... and lifestyle
Lifestyle
Lifestyle was originally coined by Austrian psychologist Alfred Adler in 1929. The current broader sense of the word dates from 1961.In sociology, a lifestyle is the way a person lives.... . Without considering these, the results could be grossly inaccurate deduction
Deduction
Deduction can refer to one of the following usages: lower price on something* Deductive reasoning, inference in which the conclusion is of no greater generality than the premises... s. Because of this, controlling unwanted variables is important in research.
Computer programming is the process of writing, testing, debugging/troubleshooting, and maintaining the source code of computer programs. This source code is written in a programming language.... , a variable is a keyword or phrase (identifier
Identifier
In computer science, Identifiers are Lexical Token s that name entity. The concept is analogy to that of a "name". Identifiers are used extensively in virtually all information processing systems.... ) that is linked to a value
Value (computer science)
In computer science, a value is a sequence of bits that is interpreted according to some data type. It is possible for the same sequence of bits to have different values, depending on the type used to interpret its meaning.... stored in the system's memory or an expression
Expression (programming)
An expression in a programming language is a combination of value s, variables, operator s, and function s that are interpreted according to the particular Order of operations and of association for a particular programming language, which computes and then produces another value.... that can be evaluated. For instance, a variable might be called 'total_count' and contain a number.
In computer science, imperative programming is a programming paradigm that describes computation in terms of statement s that change a program state .... values can generally be accessed (dereferenced) or changed (assigned
Assignment (computer science)
In computer science the assignment statement sets or re-sets the Value stored in the storage location denoted by a variable name. In most imperative programming computer programming languages the assignment statement is one of the basic Statement s.... ) at any time. In pure functional
Functional programming
In computer science, functional programming is a programming paradigm that treats computation as the evaluation of function s and avoids program state and immutable object data.... and logic language
Logic programming
Logic programming is, in its broadest sense, the use of mathematical logic for computer programming. In this view of logic programming, which can be traced at least as far back as John McCarthy 's [1958] Advice taker proposal, logic is used as a purely Declarative programming language representation language, and a automated theorem proving o... s, which have referential transparency, variables are bound
Free variables and bound variables
In mathematics, and in other disciplines involving formal languages, including mathematical logic and computer science, a free variable is a notation that specifies places in an expression where First-order_logic#Substitution may take place.... to expressions and keep a single value during their whole scope
Scope (programming)
In computer programming, scope is an enclosing context where values and expressions are associated. Various programming languages have various types of scopes.... .
C++ is a general-purpose programming language. It is regarded as a middle-level language, as it comprises a combination of both high-level programming language and low-level programming language language features.... , require strict adherence to data type
Data type
A data type in programming languages is an attribute of a data which tells the computer something about the kind of data it is. This involves setting constraints on the datum, such as what values it can take and what operations may be performed upon it.... : each variable is created with a certain type, such as integer
Integer (computer science)
In computer science, the term integer is used to refer to a data type which represents some finite subset of the mathematical integers. These are also known as integral data types.... or string
String (computer science)
In computer programming and some branches of mathematics, a string is an ordered sequence of symbols. These symbols are chosen from a predetermined set or alphabet.... , and can only store data that conforms to it. Other languages, such as JavaScript
JavaScript
JavaScript is a scripting language widely used for client-side web development. It was the originating Programming language dialect of the ECMAScript standard.... , allow variables to be treated as whatever data type is most convenient at the time. The former approach typically allows faster programming and faster execution, while the latter initially takes more time but helps prevent programming mistakes, which may eventually save time.
Naming conventions
In some programming languages, specific characters (known as sigil
Sigil (computer programming)
In computer programming, a sigil is a symbol attached to a variable name, showing the variable's datatype or Scope . The term was first applied to Perl usage by Philip Gwyn in 1999 to replace the more cumbersome "funny character in front of a variable name".... s) are prefixed or appended to variable identifiers to indicate the variable's type. For example:
In BASIC, the suffix $ on a variable name indicates that its value is a string
String (computer science)
In computer programming and some branches of mathematics, a string is an ordered sequence of symbols. These symbols are chosen from a predetermined set or alphabet.... ;
In computer programming, Perl is a high-level programming language, List of programming languages by category, Interpreter , dynamic programming language.... , the sigils $, @, %, and & indicate scalar
Scalar (computing)
In computing, a scalar is a variable or field that can hold only one value at a time; as opposed to composite variables like array, List , object composition, etc.... , array, hash, and subroutine variables, respectively.
A spreadsheet is a computer application that simulates a paper worksheet. It displays multiple cells that together make up a grid consisting of rows and columns, each cell containing either alphanumeric text or numeric values.... s variables can refer to cells (e.g. $A$2), named ranges, or values in associated source code or functions.
In computer science, source code is any collection of statements or declarations written in some human-readable computer programming language.... , a variable name is one way to bind
Name binding
In programming languages, name binding is the association of Value s with identifiers. An identifier bound to a value is said to Reference that value.... a variable to a memory location; the corresponding value is stored as a data object in that location so that the object can be accessed and manipulated later via the variable's name.
A spreadsheet is a computer application that simulates a paper worksheet. It displays multiple cells that together make up a grid consisting of rows and columns, each cell containing either alphanumeric text or numeric values.... , a cell may contain a formula
Formula
In mathematics and in the sciences, a formula is a concise way of expressing information symbolically , or a general relationship between quantities.... with references to other cells. Such a cell reference is a kind of variable; its value is the value of the referenced cell (see also: reference (computer science)
Reference (computer science)
In computer science, a reference is an object containing information about how to locate and access the particular data item, as opposed to containing the data itself.... ).
In computer programming, scope is an enclosing context where values and expressions are associated. Various programming languages have various types of scopes.... of a variable describes where in a program's text, the variable may be used, while the extent (or lifetime) describes when in a program's execution a variable has a value. The scope of a variable is actually a property of the name of the variable, and the extent is a property of the variable itself.
A variable name's scope affects its extent.
Scope is a lexical aspect of a variable. Most languages define a specific scope for each variable (as well as any other named entity), which may differ within a given program. The scope of a variable is the portion of the program code for which the variable's name has meaning and for which the variable is said to be "visible". Entrance into that scope typically begins a variable's lifetime and exit from that scope typically ends its lifetime. For instance, a variable with "lexical scope" is meaningful only within a certain block of statements or subroutine
Subroutine
In computer science, a subroutine or subprogram is a portion of computer code within a larger computer program, which performs a specific task and is relatively independent of the remaining code.... . A "global variable
Global variable
In computer programming, a global variable is a variable that is accessible in every scope . Interaction mechanisms with global variables are called global environment mechanisms.... ", or one with indefinite scope, may be referred to anywhere in the program.
Extent, on the other hand, is a runtime (dynamic) aspect of a variable. Each binding
Binding (computer science)
In computer science, binding is the creation of a simple reference to something that is larger and more complicated and used frequently. The simple reference can be used instead of having to repeat the larger thing.... of a variable to a value can have its own extent at runtime. The extent of the binding is the portion of the program's execution time during which the variable continues to refer to the same value or memory location. A running program may enter and leave a given extent many times, as in the case of a closure
Closure (computer science)
In computer science, a closure is a function that is evaluated in an environment containing one or more bound variables. When called, the function can access these variables.... .
In portions of code, a variable in scope may never have been given a value, or its value may have been destroyed. Such variables are described as "out of extent" or "unbound". In many languages, it is an error to try to use the value of a variable when it is out of extent. In other languages, doing so may yield unpredictable results. Such a variable may, however, be assigned a new value, which gives it a new extent. By contrast, it is permissible for a variable binding to extend beyond its scope, as occurs in Lisp closures and C static variable
Static variable
In computer programming, the data value of a static variable persists for the life of the running process. Typically, a static variable has a broader Scope than other variables.... s. When execution passes back into the variable's scope, the variable may once again be used.
For space efficiency, a memory space needed for a variable may be allocated only when the variable is first used and freed when it is no longer needed. A variable is only needed when it is in scope, but beginning each variable's lifetime when it enters scope may give space to unused variables. To avoid wasting such space, compilers often warn programmers if a variable is declared but not used.
It is considered good programming practice to make the scope of variables as narrow as feasible so that different parts of a program do not accidentally interact with each other by modifying each other's variables. Doing so also prevents action at a distance. Common techniques for doing so are to have different sections of a program use different namespaces, or to make individual variables "private" through either dynamic variable scoping or lexical variable scoping.
Many programming languages employ a reserved value (often named null or nil) to indicate an invalid or uninitialized variable.
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java .... or ML
ML programming language
ML is a general-purpose functional programming language developed by Robin Milner and others in the late 1970s at the University of Edinburgh, whose syntax is inspired by ISWIM.... , a variable also has a type, meaning that only values of a given class (or set of classes) can be stored in it. A variable of a primitive type holds a value of that exact primitive type. A variable of a class type can hold a null reference or a reference to an object whose type is that class type or any subclass of that class type. A variable of an interface type can hold a null reference or a reference to an instance of any class that implements the interface. A variable of an array type can hold a null reference or a reference to an array.
Python is a general-purpose high-level programming language. Its design philosophy emphasizes code readability. Python's core syntax and semantics are Minimalism , while the standard library is large and comprehensive.... , it is values, not variables, which carry type. In Common Lisp
Common Lisp
Common Lisp, commonly abbreviated CL, is a dialect of the Lisp programming language, published in American National Standards Institute standard document Information Technology - Programming Language - Common Lisp, formerly X3.226-1994 .... , both situations exist simultaneously: a variable is given a type (if undeclared, it is assumed to be T, the universal supertype
Subtype
In computer science, a subtype is a datatype that is generally related to another datatype by some notion of substitutability, meaning that computer programs written to operate on elements of the supertype can also operate on elements of the subtype.... ) which exists at compile time. Values also have types, which can be checked and queried at runtime. See type system
Type system
In computer science, a type system may be defined as "a tractable syntactic method for proving the absence of certain program behaviors by classifying phrases according to the kinds of values they compute.".... .
In computer science, polymorphism is a programming language feature that allows values of different data types to be handled using a uniform interface.... to be resolved at compile time. However, this is different from the polymorphism used in object-oriented function calls (referred to as virtual functions in C++
C++
C++ is a general-purpose programming language. It is regarded as a middle-level language, as it comprises a combination of both high-level programming language and low-level programming language language features.... ) which resolves the call based on the value type as opposed to the supertypes the variable is allowed to have.
Variables often store simple data-like integers and literal strings, but some programming languages allow a variable to store values of other datatypes as well. Such languages may also enable functions to be parametric polymorphic. These functions operate like variables to represent data of multiple types. For example, a function named length may determine the length of a list. Such a length function may be parametric polymorphic by including a type variable in its type signature
Type signature
Type signature is a term that is used in computer programming. A type signature defines the inputs and outputs for a subroutine or method .... , since the amount of elements in the list is independent of the elements' types.
Parameters
The formal parameters of functions are also referred to as variables. For instance, in this Python
Python (programming language)
Python is a general-purpose high-level programming language. Its design philosophy emphasizes code readability. Python's core syntax and semantics are Minimalism , while the standard library is large and comprehensive.... code segment,
def addtwo(x):
return x + 2
addtwo(5) # yields 7
the variable named x is a parameter because it is given a value when the function is called. The integer 5 is the argument which gives x its value. In most languages, function parameters have local scope . This specific variable named x can only be referred to within the addtwo function (though of course other functions can also have variables called x).
Memory allocation
The specifics of variable allocation and the representation of their values vary widely, both among programming languages and among implementations of a given language. Many language implementations allocate space for local variable
Local variable
In computer science, a local variable is a variable that is given local scope . Such a variable is accessible only from the subroutine or statement block in which it is declared.... s, whose extent lasts for a single function call on the call stack
Call stack
In computer science, a call stack is a dynamic Stack data structure that stores information about the active subroutines of a computer program.... , and whose memory is automatically reclaimed when the function returns. (More generally, in name binding
Name binding
In programming languages, name binding is the association of Value s with identifiers. An identifier bound to a value is said to Reference that value.... , the name of a variable is bound to the address of some particular block (contiguous sequence) of bytes in memory, and operations on the variable manipulate that block. Referencing
Reference (computer science)
In computer science, a reference is an object containing information about how to locate and access the particular data item, as opposed to containing the data itself.... is more common for variables whose values have large or unknown sizes when the code is compiled. Such variables reference the location of the value instead of the storing value itself, which is allocated from a pool of memory called the heap
Dynamic memory allocation
In computer science, dynamic memory allocation is the allocation of computer storage storage for use in a computer program during the runtime of that program.... .
Bound variables have values. A value, however, is an abstraction, an idea; in implementation, a value is represented by some data object
Object (computer science)
In its simplest embodiment, an object is an allocated region of storage. Since programming languages use variable#Computer_programmings to access objects, the terms object and variable are often used interchangeably.... , which is stored somewhere in computer memory. The program, or the runtime environment, must set aside memory for each data object and, since memory is finite, ensure that this memory is yielded for reuse when the object is no longer needed to represent some variable's value.
Objects allocated from the heap must be reclaimed specially when the objects are no longer needed. In a garbage-collected
Garbage collection (computer science)
In computer science, garbage collection is a form of automatic memory management. The garbage collector, or just collector, attempts to reclaim garbage , or memory used by Object that will never be accessed or mutated again by the Application software.... language (such as C#, Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java .... , and Lisp), the runtime environment automatically reclaims objects when extant variables can no longer refer to them. In non-garbage-collected languages, such as C
C (programming language)
C is a general-purpose computer programming language originally developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories to implement the Unix operating system.... , the program (and the programmer) must explicitly allocate
Malloc
In computing, malloc is a subroutine provided in the C and C++'s standard library for performing dynamic memory allocation.... memory, and then later free it, to reclaim its memory. Failure to do so leads to memory leak
Memory leak
In computer science, a memory leak is a particular type of unintentional memory consumption by a computer program where the program fails to release dynamic memory when no longer needed.... s, in which the heap is depleted as the program runs, risking eventual failure from exhausting available memory.
A data structure in computer science is a way of storing data in a computer so that it can be used efficiently. It is an organization of mathematical and logical concepts of data.... created dynamically, some of its components may be only indirectly accessed through the variable. In such circumstances, garbage collectors (or analogous program features in languages that lack garbage collectors) must deal with a case where only a portion of the memory reachable from the variable needs to be reclaimed.
Constants
A constant is something whose value does not change in the course of the problem under investigation. As noted above, which symbols represent variables and which represent constants is to a large extent arbitrary, and must be specified in each particular problem, though conventions about which letters stand for constants and which letters stand for variables is often assumed. (For example, most beginning students of calculus will say that the derivative of xn is nxn - 1, but this is only true under the assumption that x is a variable and n is a constant.) In a spreadsheet, in one problem it may be useful to hold DATE constant and vary COST; in another problem it may be useful to hold COST constant and vary DATE. In the first case, we might be looking at the cost of a particular item on a particular date from various vendors. In the second case we might be looking for the date on which we could buy an item for a particular price.
An assembly language is a low-level language for programming computers. It implements a symbolic representation of the numeric machine codes and other constants needed to program a particular CPU architecture.... s or instruction set specifications, constant values are termed immediate values because they are available immediately (often embedded as part of the instruction stream
Instruction (computer science)
In computer science, an instruction is a single operation of a central processing unit defined by an instruction set architecture. In a broader sense, an "instruction" may be any representation of an element of an executable program, such as a bytecode.... ) without needing to load a value from the data cache.
Although a constant value is specified only once, the constant can be referenced multiple times in a program. Using a constant instead of specifying a value multiple times in the program can not only simplify code maintenance, but it can also supply a meaningful name for it and consolidate such constant bindings to a standard code location (for example, at the beginning).
Programming languages provide one of two kinds of constant variables:
Static constant or Manifest constant
Languages such as Visual Basic allow assigning a fixed value to static constant which will be known at compile time
Compile time
In computer science, compile time refers to either the operations performed by a compiler , programming language requirements that must be met by source code for it to be successfully compiled , or properties of the program that can be reasoned about at compile time.... . Such a constant has the same value each time its program runs. Changing the value is accomplished by changing (and possibly recompiling) the code. E.g.: CONST a = 60.
Dynamic constant
Languages such as C++ and Java allow initializing a dynamic constant with a value that is computed at runtime
Runtime
In computer science, runtime or run time describes the operation of a computer program, the duration of its execution, from beginning to termination .... . Unlike static constants, the values of dynamic constants cannot be determined until run time. For example: final int a = b + 20;.
For variables which are references, do not confuse constant references with immutable object
Immutable object
In object-oriented computer programming and Functional_programming programming, an immutable object is an object whose state cannot be modified after it is created.... s. For example, when a non-constant reference references an immutable object, that reference can be changed to reference a different object, but the object it originally pointed to cannot be changed (i.e. other references that reference it still see the same information).
Conversely, a constant reference may reference a mutable object. In this case, the reference will always reference the same object (the reference cannot be changed); however, the object which is referenced can still be changed (and other references which also reference that object will see the change), as shown in the following example:
final StringBuffer sampleDynamicConstant = new StringBuffer ("InitialValueOfDynamicConstant");
sampleDynamicConstant.append("_AppendedText");
System.out.println(sampleDynamicConstant);
The above code produces the following output:
InitialValueOfDynamicConstant_AppendedText
In languages where a variable can be an object (i.e. C++), such a variable being constant is equivalent to the immutability of that object.
A naming convention is a convention for naming things. The intent is to allow useful information to be deduced from the names based on regularities.... for symbolic constants is to give them a name wherein all the letters are capitalized, sometime separated by underscores; for example: SOME_CONSTANT
Variable interpolation
Variable interpolation (also variable substitution, variable expansion) is the process of evaluating an expression or string literal containing one or more variables, yielding a result in which the variables are replaced with their corresponding values in memory. It is a specialized instance of concatenation
Concatenation
In computer programming, string concatenation is the operation of joining two character string end to end. For example, the strings "snow" and "ball" may be concatenated to give "snowball".... .
Languages that support variable interpolation include Perl
Perl
In computer programming, Perl is a high-level programming language, List of programming languages by category, Interpreter , dynamic programming language.... , PHP
PHP
PHP is a scripting language originally designed for producing dynamic web pages. It has evolved to include a command line interface capability and can be used in Standalone software Graphical user interface.... , Ruby
Ruby (programming language)
Ruby is a dynamic programming language, reflection , general purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features.... , and most Unix shell
Unix shell
A Unix shell is a command-line interpreter and script host that provides a traditional user interface for the Unix operating system and for Unix-like systems.... s. In these languages, variable interpolation only occurs when the string literal is double-quoted, but not when it is single-quoted. The variables are recognized because variables start with a sigil
Sigil (computer programming)
In computer programming, a sigil is a symbol attached to a variable name, showing the variable's datatype or Scope . The term was first applied to Perl usage by Philip Gwyn in 1999 to replace the more cumbersome "funny character in front of a variable name".... (typically "$") in these languages.
In computer programming, Perl is a high-level programming language, List of programming languages by category, Interpreter , dynamic programming language.... code:
$name = "Nancy";
print "$name said Hello World to the crowd of people.";
produces the output:
Ruby is a dynamic programming language, reflection , general purpose object-oriented programming language that combines syntax inspired by Perl with Smalltalk-like features.... uses the "#" symbol for interpolation, and lets you interpolate any expression, not just variables.
File:Train wreck at Montparnasse 1895.jpgMurphy's law is an adage in Western culture that broadly states: "Anything that can go wrong will go wrong."... predicts that constants aren't and variables don't.
In computer programming, a global variable is a variable that is accessible in every scope . Interaction mechanisms with global variables are called global environment mechanisms....
In computer science, a local variable is a variable that is given local scope . Such a variable is accessible only from the subroutine or statement block in which it is declared....
In computer programming, the data value of a static variable persists for the life of the running process. Typically, a static variable has a broader Scope than other variables....
An undefined variable in the source code of a computer program is a variable that is accessed in the code but has not been previously Declaration by that code....
An unreferenced variable in the source code of a computer program is a variable that is defined but which is never used. This may result in a harmless waste of memory ....
