"The first 5 array" should read "The first 4 array"

To add to the above, it seems that the '0' case is the culprit. If you use the code below where '10' replaces '0', the weird behavior does not occur:

$t = array(10,1,2,3,'*','+','a', 'b');
foreach($t as $v)
	switch ($v)
	{
		case 10: echo('0'); break;
		case 1: echo('1'); break;
		case 2: echo('2'); break;
		case 3: echo('3'); break;
		case '*': echo('*'); break;
		default: echo($v); break;
	}
OutPut: 0123*+ab


So it seems that Case 0: grabs all the cases which are of a different data type if the case expressions are not of the same type i.e. numeric and string.

The non-numeric string values are getting cast to integer value 0, which then match case 0:.

$t = array(10,1,2,3,'*','+','3a', 'b');
foreach($t as $v)
	switch ($v)
	{
		case 10: echo('0'); break;
		case 1: echo('1'); break;
		case 2: echo('2'); break;
		case 3: echo('3'); break;
		case '*': echo('*'); break;
		default: echo($v); break;
	}
Outputs:
0123*+3b

as 3a gets cast to 3. so seems there is a missing a condition in the code somewhere, to see if the switched expression can actually be a numeric type.


Also

$t = array(10,1,2,3,'*','+','3a', 'b');
foreach($t as $v)
	switch ($v)
	{
		case 10: echo('0'); break;
		case 1: echo('1'); break;
		case 2: echo('2'); break;
		case '*': echo('*'); break;
		case '3a': echo('!!'); break;
		default: echo($v); break;
	}
?>

Outputs:
012!!*+!!b

So the case labels are getting cast too without the check.

Oh erm, seems its not limited to switch either. :/

echo('a' == 0 ? 'YES' : 'NO');
Outputs: YES

echo('3a' == 3 ? 'YES' : 'NO');
Outputs: YES

echo(4 == '4a' ? 'YES' : 'NO');
Outputs: YES

Surely these cant be considered equivalent.

How's this for an impossibility..

echo('a' != 0 ? 'TRUE' : 'FALSE');
echo('<br />');
echo('a' ? 'TRUE' : 'FALSE');

Outputs:
FALSE
TRUE

See these manual pages:

http://www.php.net/switch
http://www.php.net/manual/en/types.comparisons.php

Maybe the manual should explain this a bit better.

The documentation does not help.

a string containing a beginning with a numeric character, but also containing non-numerics surely should not be cast to an integer before comparision?

I understand that "12345" == 12345 but the string "12345xxx" isnt 12345.

That's why you have the === operator.  "12345aaaa" has always evaluated to 12345 when cast to an integer and it always will.  That also means that it must be equivalent to 12345 when used in an integer comparison.  You need to be explicit in your comparisons and use explicit casting elsewhere.

I do understand that time has fixed this "feature".

As for explicit casting, it does result in different behaviour, when comparing string/values.

$x = '0xF';
$y = (int)$x;
echo($x == 15 ? 'YES' : 'NO');
echo('<br />');
echo($y == 15 ? 'YES' : 'NO');

Outputs:
YES
NO

Strict equivalence testing doesnt help when you wish 
"1234" and 1234 to be considered equal.

No, but if you want them to be compared as strings, just cast to a string then, or use a strcmp() call.  PHP can't read your mind.