undefined constant quantity error???

[nikko50]

This code..
$extended=$line[quantity]*$line[unitcost];

generates this notice..
Notice: Use of undefined constant quantity - assumed 'quantity'
Notice: Use of undefined constant unitcost - assumed 'unitcost'

What does this mean??

[Nate]

Quantity and unitcost are supposed to be surrounded by quotes. Otherwise PHP will first assume they are constants.