Dates and Calculating days and changing colour of row

I have Two Feilds,
DateDue
DateArrived

I want to see if the difference is more than two days and the if it is colour the row, I am doin gthis on the list page After REcord is processed.


datediff($data['DateDue'],$data['Datearrived']) as days_diff;
If days_diff > 2
$record["css"]="background:yellow;";

However I get error on the first line :

syntax error, unexpected 'as' (T_AS) in line 37