regex differentiating between ISBN-10 and ISBN-13

Question

I have an If-else statement which checks a string to see whether there is an ISBN-10 or ISBN-13 (book ID).

The problem I am facing is with the ISBN-10 check which o

Answer 1

Switch the order of the if else block, also strip all whitespace, colons, and hyphens from your ISBN:

//Replace all the fluff that some companies add to ISBNs
$str = preg_replace('/(\s+|:|-)/', '', $str);

if(preg_match("/^ISBN\d{12}(?:\d|X)$/", $str, $matches)){
   echo "ISBN-13 FOUND\n";
   //isbn returned will be 9780113411436
   return 1;
}

else if(preg_match("/^ISBN\d{9}(?:\d|X)$/", $str, $matches)){
   echo "ISBN-10 FOUND\n";  
   //isbn returned will be 9780113411
   return 0;
}