Iterating through string to find missing numbers not working

Question

The following code should print ,2,6,7,8 - At least I want it to. what the heck am I missing? The intent is to find missing numerals in a long number.

$x = 1;
$missing = "";
$newfname = "193555415493359"; 
while($x <= 9) {
    $pos = strpos($newfname,$x);
    if($pos === false) {        
        $missing .= ",$x";                  
    }
    $x++;
} 
echo $missing;

Answer 1

According to the function documentation, "If needle is not a string, it is converted to an integer and applied as the ordinal value of a character." In other words, if you pass it 9, it's looking for a tab character (ASCII 9.)

Try this instead:

$x = 1;
$missing = "";
$newfname = "193555415493359"; 
while($x <= 9) {
    $pos = strpos($newfname, (string)$x);
    if($pos === false) {        
        $missing .= ",$x";                  
    }
    $x++;
} 
echo $missing;

The only change is to cast $x as a string for the search.

Though, this could be done more efficiently:

$haystack = "193555415493359";
$needles = "123456789";
$missing = array_diff(str_split($needles), str_split($haystack));
echo implode(",", $missing);