Procedural programming

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This article is about the computer programming paradigm. For the method of algorithmic content creation, see procedural generation.

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Procedural programming can sometimes be used as a synonym for imperative programming (specifying the steps the program must take to reach the desired state), but can also refer (as in this article) to a programming paradigm based upon the concept of the procedure call. Procedures, also known as routines, subroutines, methods, or functions (not to be confused with mathematical functions, but similar to those used in functional programming) simply contain a series of computational steps to be carried out. Any given procedure might be called at any point during a program's execution, including by other procedures or itself.^[1]

Procedural programming is often a better choice than simple sequential or unstructured programming in many situations which involve moderate complexity or which require significant ease of maintainability. Possible benefits:

The ability to re-use the same code at different places in the program without copying it.
An easier way to keep track of program flow than a collection of "GOTO" or "JUMP" statements (which can turn a large, complicated program into spaghetti code).
The ability to be strongly modular or structured.

1 Procedures and modularity
2 Comparison with imperative programming
3 Comparison with object-oriented programming
4 Comparison with logic programming
5 Procedural programming languages
6 List of Some Popular Software written using Procedural Programming
7 See also
8 References
9 External links

[edit] Procedures and modularity

Modularity is generally desirable, especially in large, complicated programs. Inputs are usually specified syntactically in the form of arguments and the outputs delivered as return values.

Scoping is another technique that helps keep procedures strongly modular. It prevents the procedure from accessing the variables of other procedures (and vice-versa), including previous instances of itself, without explicit authorization.

Less modular procedures, often used in small or quickly written programs, tend to interact with a large number of variables in the execution environment, which other procedures might also modify.

Because of the ability to specify a simple interface, to be self-contained, and to be reused, procedures are a convenient vehicle for making pieces of code written by different people or different groups, including through programming libraries.

(See Module (programming) and Software package.)

[edit] Comparison with imperative programming

Most procedural programming languages are also imperative languages, because they make explicit references to the state of the execution environment. This could be anything from variables (which may correspond to processor registers) to something like the position of the "turtle" in the Logo programming language.

[edit] Comparison with object-oriented programming

The focus of procedural programming is to break down a programming task into a collection of variables, data structures, and subroutines, whereas in object oriented programming it is to break down a programming task into objects. Either method can be valid for accomplishing a specific programming task. (Object orientation is often referred to as OO and object oriented programming as OOP.)

The most popular programming languages usually have both OOP and procedural aspects.

Some differences between pure object-oriented languages and non-OO procedural languages:

pure OO	pure procedural
methods	functions
objects	modules
message	argument
attribute	variable

[edit] Comparison with logic programming

In logic programming, a program is a set of premises, and computation is performed by attempting to prove candidate theorems. From this point of view, logic programs are declarative, focusing on what the problem is, rather than on how to solve it.

However, the backward reasoning technique, implemented by SLD resolution, used to solve problems in logic programming languages such as Prolog, treats programs as goal-reduction procedures. Thus clauses of the form:

H :- B₁, …, B_n.

have a dual interpretation, both as procedures

to show/solve H, show/solve B₁ and … and B_n

and as logical implications:

B₁ and … and B_n implies H.

Experienced logic programmers use the procedural interpretation to write programs that are effective and efficient, and they use the declarative interpretation to help ensure that programs are correct.

[edit] Procedural programming languages

To be considered procedural, a programming language should support procedural programming by having an explicit concept of a procedure, and a syntax to define it. The canonical example of a procedural programming language is ALGOL.

Languages in which the only form of procedure is a method are generally considered object-oriented rather than procedural, and are not included in this list. This applies, in particular, to C# and Java.

Languages, like Prolog and its variants, which are both declarative and procedural, are also not included.