Switch is a function available in most reporting tools...Crystal, Access, VBA etc
The syntax is
Switch(expression1,var1,expression2,var2,....etc)
i.e.
Switch({dmd.type} <> "credit",
(({dstt.avg_bal}*(({?Base}-{@CrRate})/100))/365)*{dstt.num_days},
{dmd.type}="credit"...