In-depth understanding of the correct usage of PHP recursive function return values

This article introduces the correct usage of return values ​​in PHP recursive functions, and what issues need to be paid attention to when using return values ​​in PHP recursive functions, in order to deepen the understanding of PHP recursive functions.

php recursive function return value

Example, how to write return value of PHP recursive function.

Copy code Code example: 0) { $n--; return sum($n,$s); }else{ return $s; } } $sum = 0; echo sum(5,$sum);

When using php recursive functions, you will encounter problems when php recursively returns values. Usually the problem lies with the return value of a recursive function.

The original php recursive function example:

Copy code Code example:

In the above code, there is a problem in else. The test executed here has no return value. Although the entire function returns $i when the condition $i

Make the following modifications to the above PHP recursive return value function:

Copy code Code example:

2. Understanding of PHP recursive functions

The recursive function is a self-calling function. It calls itself directly or indirectly in the function body, but the conditions for self-calling need to be set. If the conditions are met, the function itself is called. If the conditions are not met, the self-calling of this function is terminated, and then the current process is The control is returned to the upper layer function for execution.

Example:

Copy code Code example: 0){ test($n-1); }else{ echo ""; } echo $n."  " } test(2) ?>

The final output of this example is 2 1 00 1 2

Analysis: The first step is to execute test(2), echo 2, and then because 2>0, execute test(1). There is still echo 2 that has not had time to execute. The second step is to execute test(1), echo 1, and then because 1>0, execute test(0). There is also echo 1 that has not had time to execute. The second step is to execute test(0), echo 0, execute test(0), echo 0. At this time, the condition of 0>0 is not met. The test() function is no longer executed, but echo "" is executed, and the following steps are executed. echo 0 At this time, the function no longer calls itself, and begins to return the control of the process to the function of the upper layer for execution, that is, it starts to execute the last echo that all the test() functions have not had time to output. The level of 0 is 1 That is to say, the upper layer of the output 1 1 is 2, that is, the output 2 2 does not have a layer above it, so the output content is 2 1 00 1 2

3. What issues should be paid attention to when using return value in PHP recursive function?

What should I do if the desired value cannot be returned correctly when using return in a PHP recursive function?

Example:

Copy code Code example: function test($i){ $i-=4; if($iWhen the above code is running, there is a problem in the else of this function. The execution result in this code has no return value. Although return $i is satisfied when the condition $i

Make the following modifications to the above PHP recursive function:

Copy code Code example: function test($i){ $i-=4; if($iIn this way, when calling the php recursive function, the required value can be returned.