Mathematical constants
There are several values in mathematics that are used in maths-related scripts but take some time to calculate, so, to save time, PHP defines them as constants available to you in every script. For example, if you want to use the value of Pi, you can just use the constant value M_PI.

For example, to calculate the area a of a circle based upon its radius r , the formula is a = pi * r 2. Using PHP we can write this as:

<?php
$area = M_PI * ( $radius * $radius );
// or...
$area = M_PI * pow ( $radius , 2 ); ?>

Using PHP's built-in maths constants saves a lot of lengthy (and pointless) calculation, so keep in mind what you have got available to you if you ever need to use mathematical constants. Here is a list of the most popular constants:

Constant

Value

Meaning

M_PI

3.14159265358979323846

Pi

M_PI_2

1.57079632679489661923

Pi/2

M_PI_4

0.78539816339744830962

Pi/4

M_1_PI

0.31830988618379067154

1/Pi

M_2_PI

0.63661977236758134308

2/Pi

M_SQRTPI

1.77245385090551602729

sqrt(M_PI)

M_2_SQRTPI

1.12837916709551257390

2/sqrt(M_PI)

M_SQRT2

1.41421356237309504880

sqrt(2)

M_SQRT3

1.73205080756887729352

sqrt(3)

M_SQRT1_2

0.70710678118654752440

1/sqrt(2)

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Jump to: Functions Functions overview How to read function prototypes Working with variables Controlling script execution Working with Date and Time Reading the current time Converting from a string Converting to a string Converting from components Mathematics Rounding Randomisation Trigonometrical conversion Other mathematical conversion functions Base conversion Mathematical constants Playing with strings Reading from part of a string Replacing parts of a string Converting to and from ASCII Measuring strings Finding a string within a string Returning the first occurrence of a string Trimming whitespace Wrapping your lines Changing string case Making a secure data hash Alternative data hashing Automatically escaping strings Pretty-printing numbers Removing HTML from a string Comparing strings Padding out a string Complex string printing Parsing a string into variables Regular expressions Basic regexps with preg_match() and preg_match_all() Novice regexps Advanced regexps Guru regexps Regular expression replacements Regular expression syntax examples The regular expressions coach Checking whether a function is available Extension functions Pausing script execution Executing external programs Connection-related functions Altering the execution environment User functions Return values Parameters Passing by reference Returning by reference Default parameters Variable parameter counts Variable scope in functions Overriding scope with the GLOBALS array Recursive functions Variable functions Callback functions The declare() function and ticks Handling non-English characters Undocumented functions Summary Exercises Further reading Next chapter

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