What categories are PHP functions divided into?

Variable function

Variable function is also called variable function. During execution, the php script will look for a function with the same name as the variable value and go to The advantage of executing it is that you can assign different function names to the same variable, assign that function name to the variable, and use the variable name plus parentheses in the program to call that function for execution.

Recursive function

Recursive function is also called a self-calling function. It will call itself during the execution process. Generally, conditions will be attached to determine whether a recursive call needs to be executed. Under certain conditions, it will Terminating the call will return the process control to the upper level function for execution. In the recursive function, if there are no additional conditions, the program will loop infinitely and cause an error.

The biggest advantage of recursive function calling is that it can simplify the complex and repeated calling procedures in the program, and this feature can be used to perform complex operations.

Custom function

php provides us with a huge function library for us to use. The function library is a design pattern in programming, and the function is a structured design. module. Functions can be used in multiple files in the same project, and functions are usually organized into one file or multiple files. These files that collect function definitions are the php function library. If you use a function defined in a function library in PHP, you need to use one of include(), include_once(), require or require_once to load the function library file into the program.

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