# PHP | pi( ) Function

While solving mathematical problems we often come across questions which requires the value of π. Manually inserting the value of PI (π) can be time-consuming and erroneous. It is also not considered as a good programming practice. To solve this issue a built-in function of PHP pi() comes to aid.

The pi() function in PHP is used to return the value of π . Also, M_PI is a named constant PHP which gives identical value to that of returned by pi() function. It is slightly faster than the pi() function.

Some other predefined named constants related to π are :

• M_PI_2 : It describes π/2. Its value is 1.570796.
• M_PI_4 : It describes π/4. Its value is 0.785398.
• M_1_PI : It describes 1/π. Its value is 0.318309.
• M_PI : It describes π. Its value is 3.141592.
• M_2_PI : It describes 2/π. Its value is 0.636619.
• M_SQRTPI : It describes sqrt(π). Its value is 1.772453.
• M_2_SQRTPI : It describes 2/sqrt(π). Its value is 1.128379.

Syntax:

`float pi()`

Parameters: This function does not accept any parameter.

Return Value: It returns a floating point value which is an approximate value of PI.

Examples:

```Input : echo(pi())
Output : 3.1415926535898

Input : echo M_PI
Output : 3.1415926535898
```

Below programs illustrate the pi() function in PHP:

1. When pi() function is used:
 ` `

Output:

`3.1415926535898`
2. When M_PI is used for finding the value of PI:
 ` `

Output:

`3.1415926535898`

Important Points To Note:

• The pi() function can be used to return the value of π.
• M_PI is a named constant which is slightly faster than the pi() function.
• pi() function returns the value of pi as float.

Reference:
http://php.net/manual/en/function.pi.php