What is a recursive function in PHP? What are the basic elements? What is its purpose? (with code)

The previous article introduced to you "What is URL.session id in PHP? What safety risks are there between them? What is the role of session id? 》, this article continues to introduce to you what is a recursive function in PHP? What are the basic elements? What is its purpose? (Code attached) This article will give you different gains. Let’s continue to explore the mysteries of PHP together! ! !

What is a recursive function:

Recursion is when a function calls itself directly or indirectly. This method of calling is called Recursive call. To put it bluntly, it's still a function call. Since it is a function call, there is an unshakable principle: all called functions will create a copy, each serving the caller without being affected by other functions.

Recursion has two basic elements:

• Boundary conditions: Determine when the recursion will terminate, also known as the recursion exit.

• Recursive mode: How large problems are decomposed into small problems, also called recursive bodies. Only if the recursive function possesses these two elements can the result be obtained after a finite number of calculations.

The purpose of recursive functions:

Recursive functions are usually used to solve the problem of structural self-similarity

Specifically, we use the code For example:

<?php
function num( $num){
echo $num;
if($num > 0){
num($num - 1);
}else{
echo &#39;<hr/>&#39;;
}
echo $num;
}
num(2);
?>

Code analysis:

First define a function num() function, then we define a $num and put it in the function function, and then we come in and output (echo) just The defined function ($num) also outputs ($num). Then we use the if statement to judge ($num>0). We perform (num-1), otherwise a horizontal line is output and (echo )$num; when we call num and pass in a 2, the output result will be the code we run (as shown below); how is the above code executed? First, we call a function of num. At this time, the value 2 we assign will be assigned to num, so the output num is 2. Then we enter the if statement to make a judgment. We will find that the function is still being called. At this time, our output is 1 is assigned to num, and the value of num is 1. By analogy, we will get the 210-012

execution result:

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