PHP Recursive Functions: How to Write Them, and Why They're Useful

Recursion Example #1: Calculating Factorials

$n = 5: Computing 5 * factorial( 4 )...
$n = 4: Computing 4 * factorial( 3 )...
$n = 3: Computing 3 * factorial( 2 )...
$n = 2: Computing 2 * factorial( 1 )...
$n = 1: Computing 1 * factorial( 0 )...
$n = 0: Base case. Returning 1...
$n = 1: Result of 1 * factorial( 0 ) = 1. Returning 1...
$n = 2: Result of 2 * factorial( 1 ) = 2. Returning 2...
$n = 3: Result of 3 * factorial( 2 ) = 6. Returning 6...
$n = 4: Result of 4 * factorial( 3 ) = 24. Returning 24...
$n = 5: Result of 5 * factorial( 4 ) = 120. Returning 120...
The factorial of 5 is: 120

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