Just revert your order of case statements and remove the break statements.
switch ($var)
{
case 'C':
$c = 3;
case 'B':
$b = 2;
case 'A':
$a = 1;
break;
}
From the manual:
It is important to understand how the switch statement is executed in
order to avoid mistakes. The switch statement executes line by line
(actually, statement by statement). In the beginning, no code is
executed. Only when a case statement is found with a value that
matches the value of the switch expression does PHP begin to execute
the statements. PHP continues to execute the statements until the end
of the switch block, or the first time it sees a break statement. If
you don't write a break statement at the end of a case's statement
list, PHP will go on executing the statements of the following case.