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PHP has hundreds of base functions and thousands more from extensions. Prior to PHP version 5.3.0, functions are not first-class functions and can only be referenced by their name, whereas PHP 5.3.0 introduces closures. [35] User-defined functions can be created at any time and without being prototyped. [35]
Even when using numerical indexes, PHP internally stores arrays as associative arrays. [13] So, PHP can have non-consecutively numerically indexed arrays. The keys have to be of integer (floating point numbers are truncated to integer) or string type, while values can be of arbitrary types, including other arrays and objects.
A vector treated as an array of numbers by writing as a row vector or column vector (whichever is used depends on convenience or context): = (), = Index notation allows indication of the elements of the array by simply writing a i, where the index i is known to run from 1 to n, because of n-dimensions. [1]
The subscripts and superscripts are set in upright font, in keeping with normal practice for numerals and descriptive subscripts. To set the superscript or subscript in oblique font, as for a subscript that itself is a variable, use the HTML <var>...</var> or <i>...</i> tags, or the wikimarkup for italics ('').
The most common superscript digits (1, 2, and 3) were included in ISO-8859-1 and were therefore carried over into those code points in the Latin-1 range of Unicode. The remainder were placed along with basic arithmetical symbols, and later some Latin subscripts, in a dedicated block at U+2070 to U+209F. The table below shows these characters ...
In C and C++ arrays do not support the size function, so programmers often have to declare separate variable to hold the size, and pass it to procedures as a separate parameter. Elements of a newly created array may have undefined values (as in C), or may be defined to have a specific "default" value such as 0 or a null pointer (as in Java).
Superscripts and Subscripts is a Unicode block containing superscript and subscript numerals, mathematical operators, and letters used in mathematics and phonetics. The use of subscripts and superscripts in Unicode allows any polynomial, chemical and certain other equations to be represented in plain text without using any form of markup like HTML or TeX.
Do not use the Unicode subscripts and superscripts ² and ³, or XML/HTML character entity references (² etc.). Rather, write <sup>2</sup> and <sup>3</sup> to produce the superscripts 2 and 3. The superscripted 2 and 3 are easier to read, especially on small displays, and ensure that exponents are properly aligned. Compare: