Learn PHP Built in Functions:
Php built in functions are those functions which are pre-defined in library of php . Which are ready to use in php by default like most common php functions , php arrray, php array to string , php multidimensional array .
PHP comes standard with many functions and constructs. There are also functions that require specific PHP extensions compiled in, otherwise fatal \”undefined function\” errors will appear. For example, to use image functions such as imagecreatetruecolor(), PHP must be compiled with GD support. Or, to use mysqli_connect(), PHP must be compiled with MySQLi support. There are many core functions that are included in every version of PHP, such as the string and variable functions. A call to phpinfo() or get_loaded_extensions() will show which extensions are loaded into PHP. Also note that many extensions are enabled by default and that the PHP manual is split up by extension. See the configuration, installation, and individual extension chapters, for information on how to set up PHP.