Nesting (computing)
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In
computing science Computer science is the study of computation, information, and automation. Computer science spans theoretical disciplines (such as algorithms, theory of computation, and information theory) to applied disciplines (including the design an ...
and
informatics Informatics is the study of computational systems. According to the Association for Computing Machinery, ACM Europe Council and Informatics Europe, informatics is synonymous with computer science and computing as a profession, in which the centra ...
, nestinghttps://study.com/academy/lesson/nesting-loops-stan C Programming is where information is organized in layers, or where
object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an a ...
s contain other similar objects. It almost always refers to
self-similar In mathematics, a self-similar object is exactly or approximately similar to a part of itself (i.e., the whole has the same shape as one or more of the parts). Many objects in the real world, such as coastlines, are statistically self-similar ...
or
recursive Recursion occurs when the definition of a concept or process depends on a simpler or previous version of itself. Recursion is used in a variety of disciplines ranging from linguistics to logic. The most common application of recursion is in m ...
structures in some sense.


Terminology

Nesting can mean: * nested calls: ** using several levels of
subroutine In computer programming, a function (also procedure, method, subroutine, routine, or subprogram) is a callable unit of software logic that has a well-defined interface and behavior and can be invoked multiple times. Callable units provide a ...
s ** recursive calls * nested levels of parentheses in arithmetic expressions * nested blocks of imperative
source code In computing, source code, or simply code or source, is a plain text computer program written in a programming language. A programmer writes the human readable source code to control the behavior of a computer. Since a computer, at base, only ...
such as nested if-clauses, while-clauses, repeat-until clauses etc. *
information hiding In computer science, information hiding is the principle of segregation of the ''design decisions'' in a computer program that are most likely to change, thus protecting other parts of the program from extensive modification if the design decisio ...
: ** nested function definitions with
lexical scope In computer programming, the scope of a name binding (an association of a name to an entity, such as a variable) is the part of a program where the name binding is valid; that is, where the name can be used to refer to the entity. In other parts ...
** nested data structures such as records, objects, classes, etc. *
nested virtualization In computing, virtualization (abbreviated v12n) is a series of technologies that allows dividing of physical computing resources into a series of virtual machines, operating systems, processes or containers. Virtualization began in the 1960s with ...
, also called recursive virtualization: running a
virtual machine In computing, a virtual machine (VM) is the virtualization or emulator, emulation of a computer system. Virtual machines are based on computer architectures and provide the functionality of a physical computer. Their implementations may involve ...
inside another virtual machine


In spreadsheets

In a
spreadsheet A spreadsheet is a computer application for computation, organization, analysis and storage of data in tabular form. Spreadsheets were developed as computerized analogs of paper accounting worksheets. The program operates on data entered in c ...
functions can be ''nested'' one into another, making complex formulas. The function wizard of the
OpenOffice.org OpenOffice.org (OOo), commonly known as OpenOffice, is a discontinued open-source office suite. Active successor projects include LibreOffice (the most actively developed) and Collabora Online, with Apache OpenOffice being considered mostly d ...
Calc application allows to navigate through multiple levels of nesting, letting the user to edit (and possibly correct) each one of them separately. For example: =IF(SUM(C8:G8)=0,"Y","N") In this
Microsoft Excel Microsoft Excel is a spreadsheet editor developed by Microsoft for Microsoft Windows, Windows, macOS, Android (operating system), Android, iOS and iPadOS. It features calculation or computation capabilities, graphing tools, pivot tables, and a ...
formula, the SUM function is nested inside the IF function. First, the formula calculates the sum of the numbers in the cells from C8 to G8. It then decides whether the sum is 0, and it displays the letter Y if the sum is 0, and the letter N if it is not. Naturally, to allow the mathematical resolution of these chained (or better: ''nested'') formulas, the inner expressions must be previously evaluated, and this outward direction is essential because the results that the ''internal'' functions return are temporarily used as entry data for the ''external'' ones. Due to the potential accumulation of parentheses in only one code line, editing and error detecting (or
debugging In engineering, debugging is the process of finding the Root cause analysis, root cause, workarounds, and possible fixes for bug (engineering), bugs. For software, debugging tactics can involve interactive debugging, control flow analysis, Logf ...
) can become somehow ''awkward''. That is why modern programming environments -as well as spreadsheet programs- highlight in bold type the pair corresponding to the current editing position. The (automatic) balancing control of the opening and closing parenthesis is known as ''brace match checking''.


In programming


Control structures

In
structured programming Structured programming is a programming paradigm aimed at improving the clarity, quality, and development time of a computer program by making specific disciplined use of the structured control flow constructs of selection ( if/then/else) and repet ...
languages, ''nesting'' is related to the ''enclosing'' of
control structures In computer science, control flow (or flow of control) is the order in which individual statements, instructions or function calls of an imperative program are executed or evaluated. The emphasis on explicit control flow distinguishes an '' ...
one into another, usually indicated through different ''indentation'' levels within the
source code In computing, source code, or simply code or source, is a plain text computer program written in a programming language. A programmer writes the human readable source code to control the behavior of a computer. Since a computer, at base, only ...
, as it is shown in this simple
BASIC Basic or BASIC may refer to: Science and technology * BASIC, a computer programming language * Basic (chemistry), having the properties of a base * Basic access authentication, in HTTP Entertainment * Basic (film), ''Basic'' (film), a 2003 film ...
function: function LookupCode(sCode as string) as integer dim iReturnValue as integer dim sLine, sPath as string sPath="C:\Test.dsv" if FileExists(sPath) then open sPath for input as #1 do while not EOF(1) line input #1, sLine if sCode=left(sLine, 3) then 'Action(s) to be carried out End if loop close #1 End if LookupCode=iReturnValue end function In this small and simple example, the conditional block “if... then... end if” is nested inside the “do while... loop” one. Some languages such as Pascal and Ada have no restrictions on declarations depending on the nesting level, allowing precisely nested subprograms or even nested packages (Ada). Here is an example of both (simplified from a real case): -- Getting rid of the global variables issue (cannot be used in parallel) -- from a set of old sources, without the need to change that code's -- logic or structure. -- procedure Nesting_example_1 is type Buffer_type is array(Integer range <>) of Integer; procedure Decompress( compressed : in Buffer_type; decompressed: out Buffer_type ) is -- Here are the legacy sources, translated: package X_Globals is index_in, index_out: Integer; -- *** ^ These variables are local to Decompress. -- *** Now Decompress is task-safe. end X_Globals; -- Methods 1,2,3,... (specifications) package X_Method_1 is procedure Decompress_1; end X_Method_1; -- Methods 1,2,3,... (code) package body X_Method_1 is use X_Globals; procedure Decompress_1 is begin index_in:= compressed'First; -- Here, the decompression code, method 1 end Decompress_1; end X_Method_1; -- End of the legacy sources begin X_Method_1.Decompress_1; end Decompress; test_in, test_out: Buffer_type(1..10_000); begin Decompress(test_in, test_out); end Nesting_example_1;


Data structures

Nested
data structures In computer science, a data structure is a data organization and storage format that is usually chosen for efficient access to data. More precisely, a data structure is a collection of data values, the relationships among them, and the functi ...
are also commonly encountered in programming.


Lisp

In the
functional programming In computer science, functional programming is a programming paradigm where programs are constructed by Function application, applying and Function composition (computer science), composing Function (computer science), functions. It is a declarat ...
languages, such as
Lisp Lisp (historically LISP, an abbreviation of "list processing") is a family of programming languages with a long history and a distinctive, fully parenthesized Polish notation#Explanation, prefix notation. Originally specified in the late 1950s, ...
, a
list A list is a Set (mathematics), set of discrete items of information collected and set forth in some format for utility, entertainment, or other purposes. A list may be memorialized in any number of ways, including existing only in the mind of t ...
data structure exists as does a simpler
atom Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...
data structure. *Simple lists hold only atoms. ( A T O M S ) The atoms in the list are A, T, O, M, and S. *Nested lists hold both atoms and other lists. ( ( ( N E S T E D ) L I S T S ) ( C A N ) ( B E ) U N N E C E S S A R I L Y ( C O M P L E X ) )


See also

* Flow control *
For loop In computer science, a for-loop or for loop is a control flow Statement (computer science), statement for specifying iteration. Specifically, a for-loop functions by running a section of code repeatedly until a certain condition has been satisfi ...
*
Pseudocode In computer science, pseudocode is a description of the steps in an algorithm using a mix of conventions of programming languages (like assignment operator, conditional operator, loop) with informal, usually self-explanatory, notation of actio ...
*
Structured programming Structured programming is a programming paradigm aimed at improving the clarity, quality, and development time of a computer program by making specific disciplined use of the structured control flow constructs of selection ( if/then/else) and repet ...


References

{{reflist Computer data Computer programming