i need to create a crystal report for user to print the month end data. but now i facing some issue on writing formula code.

i create parameter field allow user select either "Current period", "previous period 1" and "previous period 2".

when user select "current period" in parameter field, the report title will show out the date of this month end, if user select "previous period 1" then report title will show out the date of previous month end.

Example:

Current month is October 2009

Users print this report on 15/10/2009.

If users print trial balance as of current period, report title will show out “31 October 2009”  or show "31/10/2009"

If users print trial balance as of previous period 1, report title will show out “30 September 2009” or show "30/09/2009"

If users print trial balance as of previous period 2, report title will show out “31 August 2009” or show "31/08/2009"

May i know how to write a formula on this issue?

*the coding i write currently as below:

select {APAgedTrialBalanceReport/QueryOptions.ReportAsOf}
    case 'C':
    ToText (PrintDate)      <-this on can show the print date
    case 'P1':
    "XXX1"          <- temporally hard code because don't know how to write code?
    case 'P2':
    "XXX2"          <- temporally hard code because don't know how to write code?

Thank you.