I have an php array of 99 numbers.
The array contains the digits 1 to 100 with one digit missing.
How to know the missing number?
Since you say you've found an answer yourself, here is a possible solution
$assignmentArray = array(1,2,3,4,5,6,7,8,10);
// find the missing fie... err.. missing value is actually more correct.
$missingNumber = array_sum(range(1, 10)) - array_sum($assignmentArray);
echo 'The missing number is: ' . $missingNumber;