外行人的术语是使用PHP的递归函数

Question

Can anyone please explain a recursive function to me in PHP (without using Fibonacci) in layman language and using examples? i was looking at an example but the Fibonacci totally lost me!

Thank you in advance ;-) Also how often do you use them in web development?

Answer 1

Laymens terms:

A recursive function is a function that calls itself

A bit more in depth:

If the function keeps calling itself, how does it know when to stop? You set up a condition, known as a base case. Base cases tell our recursive call when to stop, otherwise it will loop infinitely.

What was a good learning example for me, since I have a strong background in math, was factorial. By the comments below, it seems the factorial function may be a bit too much, I'll leave it here just in case you wanted it.

function fact($n) {
  if ($n === 0) { // our base case
     return 1;
  }
  else {
     return $n * fact($n-1); // <--calling itself.
  }
}

In regards to using recursive functions in web development, I do not personally resort to using recursive calls. Not that I would consider it bad practice to rely on recursion, but they shouldn't be your first option. They can be deadly if not used properly.

Although I cannot compete with the directory example, I hope this helps somewhat.

(4/20/10) Update:

It would also be helpful to check out this question, where the accepted answer demonstrates in laymen terms how a recursive function works. Even though the OP's question dealt with Java, the concept is the same,

• Understanding basic recursion