Recursion

Example in PHP using the factorial:

1. // $n must be a positive integer or 0 - function returns 1 for 0 and all errors

2. function factorial($n)

3. {

4.   if ($n > 0 && is_int($n))

5.   {

6.     // factorial of positive integer

7.     return $n * factorial($n - 1);

8.   } else

9.   {

10.     // factorial of 0

11.     return 1;

12.   }

13. }

There are many other blog posts that cover this topic well. Some include:

Recursion in PHP (and iteration)

Recursive patterns in Regex from the PHP manual

Here is a little snippet of a C++ function that will ask for user input and make sure it is a float. If it’s not a float, the functions recurses (is that a word?)… calls itself. The end effect is that the user is asked to enter a float until they do. You must include both iostream and limits.

1. float collectFloat()

2. {

3.   float user_input(0.0);

4.   try

5.   {

6.     // Could also use cin.fail() to check for success

7.     if (cin >> user_input) cinIgnoreRest();

8.     else

9.       throw (string(“\nNot a float entered.\n Please enter a number.\n”));

10.   }

11.   catch (string error)

12.   {

13.     cout << error << “==> “;

14.     cin.clear();

15.     cinIgnoreRest();

16.     // This will keep repeating until user enters a float

17.     user_input = collectFloat();

18.   }

19.     return user_input;

20. }

Tags: PHP, recursion

This entry was posted on Monday, March 29th, 2010 at 4:44 pm and is filed under PHP. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.