Programming style

Guidelines when writing computer code

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Programming style, also known as coding style or code style, is a set of rules or guidelines that governs the layout of source code. Programming style may also refer a quality aspect of code that is interpreted subjectively.

Some claim that following a particular programming style helps programmers read and understand code and to avoid introducing errors.

The Elements of Programming Style, written in the 1970s provides examples in Fortran and PL/I.

The style used in a particular codebase is often based on the coding conventions of a company or organization, or the preferences of the programmer.

A style is often designed for a specific programming language or language family. For example, a style used for C may not be appropriate for BASIC. However, some rules are applied to many languages.

## Automation[edit]

Tools are available that format source code, leaving coders to concentrate other aspects such as logic and naming. Using such tools can save development time and achieve a high level of consistency.

## Style aspects[edit]

Aspects of code style include but are limited to:

* Indentation and other white space
* Naming of user-defined identifiers
* Capitalization of keywords (when allowed by the language)
* Use of comments

### Indentation[edit]

Indentation style can assist a reader in various way including: identifying control flow and blocks of code. In some programming languages, indentation is used to delimit blocks of code and therefore is not matter of style. In languages that ignore white space, indentation can affect readability.

For example, formatted in a commonly-used style:

if (hours < 24 && minutes < 60 && seconds < 60) {
return true;
} else {
return false;

Arguably, poorly formatted:

if  ( hours   < 24
&& minutes < 60
&& seconds < 60

{return    true
;}         else
{return   false

#### Notable indentation styles[edit]

##### ModuLiq[edit]

The ModuLiq Zero Indentation Style groups by empty line rather than indentation.

Example:

if (hours < 24 && minutes < 60 && seconds < 60)
return true;

else
return false;

##### Lua[edit]

Lua does not use the traditional curly braces or parentheses; rather, the expression in a conditional statement must be followed by `then`, and the block must be closed with `end`.

if hours < 24 and minutes < 60 and seconds < 60 then
return true
else
return false
end

Indentation is optional in Lua. `and`, `or`, and `not` function as logical operators.

##### Python[edit]

Python relies on indentation to indicate control structure, thus eliminating the need for bracketing (i.e. `{` and `}`). On the other hand, copying and pasting Python code can lead to problems, because the indentation level of the pasted code may not be the same as the indentation level of the current line. Such reformatting can be tedious to do by hand, but some text editors and IDEs have features to do it automatically. There are also problems when Python code being rendered unusable when posted on a forum or web page that removes white space, though this problem can be avoided where it is possible to enclose code in white space-preserving tags such as "<pre> ... </pre>" (for HTML), "[code]" ... "[/code]" (for bbcode), etc.

if hours < 24 and minutes < 60 and seconds < 60:
return True
else:
return False

Notice that Python starts a block with a colon (`:`).

Python programmers tend to follow a commonly agreed style guide known as PEP8.[1] There are tools designed to automate PEP8 compliance.

##### Haskell[edit]

Like Python, Haskell has the off-side rule. It has a two-dimension syntax where indentation is meaningful to define blocks (although, an alternate syntax uses curly braces and semicolons).

Haskell is a declarative language, there are statements, but declarations within a Haskell script.

Example:

let c_1 = 1
c_2 = 2

f x y = c_1 * x + c_2 * y

may be written in one line as:

let {c_1=1;c_2=2}
in f x y = c_1 * x + c_2 * y

Haskell encourages the use of literate programming, where extended text explains the genesis of the code. In literate Haskell scripts (named with the `lhs` extension), everything is a comment except blocks marked as code. The program can be written in LaTeX, in such case the `code` environment marks what is code. Also, each active code paragraph can be marked by preceding and ending it with an empty line, and starting each line of code with a greater than sign and a space. Here an example using LaTeX markup:

The function \verb+isValidDate+ test if date is valid
\begin{code}
isValidDate :: Date -> Bool
isValidDate date = hh>=0  && mm>=0 && ss>=0
&& hh<24 && mm<60 && ss<60
where (hh,mm,ss) = fromDate date
\end{code}
observe that in this case the overloaded function is \verb+fromDate :: Date -> (Int,Int,Int)+.

And an example using plain text:

The function isValidDate test if date is valid

> isValidDate :: Date -> Bool
> isValidDate date = hh>=0  && mm>=0 && ss>=0
>                  && hh<24 && mm<60 && ss<60
>  where (hh,mm,ss) = fromDate date

observe that in this case the overloaded function is fromDate :: Date -> (Int,Int,Int).

### Vertical alignment[edit]

Some programmers consider it valuable to align similar elements vertically (as tabular, in columns), citing that it can make typo-generated bugs more obvious.

For example, unaligned:

$search = array('a', 'b', 'c', 'd', 'e');
$replacement = array('foo', 'bar', 'baz', 'quux');

$value = 0;
$anothervalue = 1;
$yetanothervalue = 2;

aligned:

$search      = array('a',   'b',   'c',   'd',   'e');
$replacement = array('foo', 'bar', 'baz', 'quux');

$value           = 0;
$anothervalue    = 1;
$yetanothervalue = 2;

Unlike the unaligned code, the aligned code implies that the search and replace values are related since they have corresponding elements. As there is one more value for search than replacement, if this is a bug, it is more likely to be spotted via visual inspection.

Cited disadvantages of vertical alignment include:

* Dependencies across lines which leads to maintenance load. For example, if a long column value is added that requires a wider column, then all lines of the table must be modified (to maintain the tabular form) which is a larger change which leads to more effort to review and to understand the change at a later date
* Brittleness: if a programmer does not correctly format the table when making a change, the result is a visual mess that is harder to read than unaligned code. Simple refactoring operations, such as renaming, can break the formatting.
* More effort to maintain which may discourage a programmer from making a beneficial change, such as improving the name of an identifier, because doing so would require significant formatting effort
* Requirement to use a fixed-width fonts; not proportional fonts

Maintaining alignment can be alleviated by a tool that provides support (i.e. for elastic tabstops), although that creates a reliance on such tools.

As an example, simple refactoring operations to rename "$replacement" to "$r" and "$anothervalue" to "$a" results in:

$search      = array('a',   'b',   'c',   'd',   'e');
$r = array('foo', 'bar', 'baz', 'quux');

$value           = 0;
$a    = 1;
$yetanothervalue = 2;

With unaligned formatting, these changes do not have such a dramatic, inconsistent or undesirable effect:

$search = array('a', 'b', 'c', 'd', 'e');
$r = array('foo', 'bar', 'baz', 'quux');

$value = 0;
$a = 1;
$yetanothervalue = 2;

### White space[edit]

A free-format language ignores white space: spaces, tabs and new lines so the programmer is free to style the code in different ways without affecting the meaning of the code. Generally, the programmer uses style that is considered to enhance readability.

The following two code snippets are the same logically, but differ in white space.

int i;
for(i=0;i<10;++i){
printf("%d",i*i+i);

versus

int i;
for (i = 0; i < 10; ++i) {
printf("%d", i * i + i);

The use of tabs for white space is debatable. Alignment issues arise due to differing tab stops in different environments and mixed use of tabs and spaces.

As an example, one programmer prefers tab stops of four and has their toolset configured this way, and uses these to format their code.

int     ix;     // Index to scan array
long    sum;    // Accumulator for sum

Another programmer prefers tab stops of eight, and their toolset is configured this way. When someone else examines the original person's code, they may well find it difficult to read.

int             ix;             // Index to scan array
long    sum;    // Accumulator for sum

One widely used solution to this issue may involve forbidding the use of tabs for alignment or rules on how tab stops must be set. Note that tabs work fine provided they are used consistently, restricted to logical indentation, and not used for alignment:

class MyClass {
int foobar(
int qux, // first parameter
int quux); // second parameter
int foobar2(
int qux, // first parameter
int quux, // second parameter
int quuux); // third parameter

## See also[edit]

* Coding conventions
* MISRA C
* Naming convention (programming)

## References[edit]

1. ^ "PEP 0008 -- Style Guide for Python Code". python.org.

## External links[edit]

* Source Code Formatters at Curlie