Editing Decimal separator (section)

===Data vis-à-vis mask===
Digit group separators can occur either as part of the data or as a mask through which the data is displayed. This is an example of the [[separation of presentation and content]], making it possible to display numbers in spaced groups while not inserting any [[whitespace character]]s into the string of digits that make up those numbers. In many computing contexts, it is preferred to omit the digit group separators from the data and instead overlay them as a mask (an [[input mask]] or an output mask).

Common examples include [[spreadsheet]]s and [[database]]s, in which currency values are entered without such marks but are displayed with them inserted. Similarly, phone numbers can have hyphens, spaces or parentheses as a mask rather than as data. In [[web content]], digit grouping can be done with [[CSS]]. This is useful because the number can be copied and pasted elsewhere (such as into a calculator) and parsed by the computer as-is (i.e., without the user manually purging the extraneous characters). For example:
{{block indent |left=1.5 |text={{plainlist}}
* {{val|149597870700}} metres is 1 [[astronomical unit]].
* {{gaps|3.14159|26535|89793|23846}} is [[pi|{{pi}}]] rounded to 20 decimal places.
* {{gaps|2.71828|18284|59045|23536}} is {{mvar|[[E (mathematical constant)|e]]}} rounded to 20 decimal places.
{{endplainlist}}}}

In some [[programming language]]s, it is possible to group the digits in the program's [[source code]] to make it easier to read {{xref|(see: {{slink|Integer literal#Digit separators}})}}. Examples include: [[Ada programming language|Ada]], [[C Sharp (programming language)|C#]] (since {{nobr|version 7.0}}),<ref>{{cite report |title=New Features in C#&nbsp;77.0 |section=Literal improvements |date=9 March 2017 |publisher=Microsoft |type=blog |section-url=https://devblogs.microsoft.com/dotnet/new-features-in-c-7-0/#literal-improvements |access-date=5 May 2022}}</ref> [[D (programming language)|D]], [[Go (programming language)|Go]] (since {{nobr|version 1.13}}), [[Haskell (programming language)|Haskell]] (from GHC {{nobr|version 8.6.1}}), [[Java (programming language)|Java]], [[JavaScript]] (since [[ECMAScript version history#12th Edition – ECMAScript 2021|ES2021]]), [[Kotlin (programming language)|Kotlin]],<ref>{{cite web |title=Basic types |website=Kotlin Language |url=https://kotlinlang.org/docs/basic-types.html#literal-constants:~:text=You%20can%20use%20underscores%20to%20make%20number%20constants%20more%20readable}}</ref> [[OCaml]], [[Perl]], [[Python (programming language)|Python]] (since {{nobr|version 3.6}}), [[PHP]] (since {{nobr|version 7.4}}),<ref>{{cite web |series=PHP: New Features |title=Numeric literal separator |publisher=The PHP Group |url=https://www.php.net/manual/en/migration74.new-features.php#migration74.new-features.core.numeric-literal-separator |access-date=2020-07-16}}</ref> [[Ruby (programming language)|Ruby]], [[Rust (programming language)|Rust]] and [[Zig (programming language)|Zig]].

Java, JavaScript, [[Swift (programming language)|Swift]], [[Julia (programming language)|Julia]] and free-form [[Fortran 90]] use the [[underscore]] ({{code|_}}) character for this purpose. As such, these languages would allow the number seven hundred million to be entered as "700_000_000". On the other hand, fixed-form Fortran ignores whitespace in all contexts, so "{{nobr|700 000 000}}" would be allowed. In [[C++14]], [[Rebol]] and [[Red (programming language)|Red]], the use of an [[apostrophe]] for digit grouping is allowed. Thus, "700'000'000" would be allowed in those languages.

The code shown below, written in Kotlin, illustrates the use of separators to increase readability:
<syntaxhighlight lang="kotlin" line="1">
val exampleNumber = 12_000_000 // twelve million
</syntaxhighlight>