Common computer terms and definitions

Here are some summarized computer terms with short definitions. There are exceptions to almost everything, but these short definitions are useful to commit to quick-access memory when programming.

A type is a set of allowable values.

Some common programming types are integer, Boolean, character, string, and floating point approximations.

Short definition: type = set of allowable values

A literal is an expressly written entity.

Short definition: literal = expressly written entity

A literal value literally expresses a value. The word comes from the Latin that means "letter", as in "letter of the law".

The word "entity" is a nice way to say "thing" or "something".

A constant is a named literal.

Short definition: constant = named literal

In mathematics, a constant is something that never changes.
In physics, a constant is something that is assumed not to change.
In programming, a constant is a name given to a literal value.

A variable is a named storage location that contains the value of the variable.

Short definition: variable = named storage location

In mathematics, a variable is a placeholder for a value to be supplied (like a computer formal parameter).

A declaration is a way to request memory storage for a variable name.

Short definition: declaration = reservation of storage by name

When you "declare" something, like the "Declaration of Independence", you state that something is what you want it to be.

An expression is a formula that evaluates to and can be expressed as a literal value.

Short definition: expression = formula that evaluates to a literal value

The word "expression" comes from the Latin and means, literally, to "press out", as someone who has an expression on their face.

A mathematical formula is what in programming is called an expression.
Expressions are evaluated for a value, not executed for an effect.

A statement is a command that is executed for effect.

Short definition: statement = command executed of effect

Statements are executed, not evaluated.
Banks send statements to customers each month (paper or paperless).

An assignment statement destructively moves data around computer memory.

Short definition: assignment = way to move data around in memory

An assignment statement has a variable on the LHS (Left Hand Side) , an expression on the RHS (Right Hand Side) , and is executed in two steps.

1. Evaluate the expression on the RHS to a (literal) value.
2. Store the value into the memory location represented by variable on the LHS , destroying whatever value was previously in that location.

This operation is known as a destructive update as the value is gone forever.

A procedure allows repeated statements to be shared, acting as a statement that is called for effect.

Effect means that something is changed. This something sometimes called a side-effect.

In some languages, a procedure is a function that returns nothing.
A general term for a procedure or function is a routine.

Short definition: procedure = acts as a command of repeated commands and called for effect

A function allows repeated expressions to be shared, acting as an expression that is called to provide a value.

Short definition: function = acts as formula of repeated formulas and called for a value

In mathematics, a function takes arguments and return one value and has no side-effects.
In programming, a function can (usually) return more than one value and can have side-effects.
In some programming languages, a function that returns nothing is called a procedure.
A general term for a procedure or function is a routine.

A formal parameter is a name that acts as a placeholder in a function or procedure for an actual value to be supplied when the function or procedure is called.

Short definition: formal parameter = name that acts as a placeholder value to be supplied

In mathematics, a variable is what in programming is called a formal parameter.
In mathematics, an argument is in programming called a parameter.

An actual parameter supplies an actual value to be matched with the corresponding formal parameter in the procedure or function when the procedure or function is called.

Short definition: actual parameter = supplies an existing value matched with a parameter

In mathematics, an argument is in programming called a parameter.

A value parameter is a formal parameter whose corresponding actual parameter value is passed to a procedure or function

A routine with a value parameter is said to use call by value (for that parameter).

If the actual parameter represents a memory location (e.g., a variable), assigning a value to the formal parameter within the procedure or function does not change the contents of the memory location represented by the actual parameter. A copy of the value is passed.

Short definition: value parameter = copy is supplied to the called routine

A reference parameter is a formal parameter whose actual parameter represents a memory location.

A routine with a reference parameter is said to use call by reference (for that parameter).

So assigning a value to the formal parameter within the procedure or function changes the contents of the memory location represented by the actual parameter.

Short definition: reference parameter = location is supplied to the called routine

A global variable is a variable that can be directly accessed by using its name from anywhere in a program/class.

In some languages, a local variable with the same name can hide the global variable.

Short definition: global variable = can be accessed from anywhere in the program

A local variable is a variable that can only be directly accessed by name within the procedure/function in which it is defined.

A formal parameter is treated as a variable local to the procedure/function/block in which it is declared.

Short definition: local variable = only available within a routine or block of code

An array is a structured data type consisting of elements of the same type that are accessed by an index expression.

Short definition: array = structured data type of elements of one type accessed by an index expression

A record is a structured data type consisting of elements called fields of varying data types that are accessed by name.

Short definition: record = structured data type of elements called fields of varying types accessed by name

An object is an instance of a class.

Short definition: object = instance of a blueprint

A class is a general blueprint used to create instances.

Short definition: class = blueprint for making instances

Here is a summary of the above terms using the quick definitions.

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