If you want to use something like the switch variable in the categories tag you can use this php snippet
<?php echo ({count} % 2)? "row_one" : "row_two"; ?>
the result returns 1 or 0, so it is always true or false, “row_one” or “row_two”.
When you need more then 2 different row styles you can increase the integer but you will need a switch statement, like
<?php
switch ({count} % 5){
case 1:
echo "row_one";
break;
case 2:
echo "row_two";
break;
case 3:
echo "row_three";
break;
case 4:
echo "row_four";
break;
default:
echo "row_five";
break;
}
?>