Editing Structured programming (section)

==Elements==

===Control structures===
Following the [[structured program theorem]], all programs are seen as composed of three [[control structure]]s:
* "Sequence"; ordered statements or subroutines executed in sequence.
* "Selection"; one of a number of statements is executed depending on the state of the program. This is usually expressed with [[Keyword (computer programming)|keyword]]s such as [[Conditional (programming)|<code>if..then..else..endif</code>]]. The conditional statement should have at least one true condition and each condition should have one exit point at max.
* "Iteration"; a statement or block is executed until the program reaches a certain state, or operations have been applied to every element of a collection.  This is usually expressed with keywords such as [[While loop|<code>while</code>]], [[Do while loop|<code>repeat</code>]], [[For loop|<code>for</code>]] or [[Do while loop|<code>do..until</code>]]. Often it is recommended that each loop should only have one entry point (and in the original structural programming, also only one exit point, and a few languages enforce this).

[[File:Structured_program_patterns.svg|thumb|649x649px|center|Graphical representation of the [[structured program theorem|three basic patterns]] — sequence, selection, and repetition — using [[Nassi–Shneiderman diagram|NS diagrams]] (blue) and [[flow chart]]s (green).]]

===Subroutines===
[[Subroutine]]s; callable units such as procedures, functions, methods, or subprograms are used to allow a sequence to be referred to by a single statement.

===Blocks===
[[Block (programming)|Blocks]] are used to enable groups of statements to be treated as if they were one statement. ''Block-structured'' languages have a syntax for enclosing structures in some formal way, such as an if-statement bracketed by <code>if..fi</code> as in [[ALGOL 68]], or a code section bracketed by <code>BEGIN..END</code>, as in [[PL/I]] and [[Pascal (programming language)|Pascal]], [[whitespace character|whitespace]] indentation as in [[Python (programming language)|Python]], or the curly braces <code>{...}</code> of [[C (programming language)|C]] and [[Curly brace family#Curly-bracket languages|many later languages]].