What would the VBA be to execute This?

Generate case Number When case form Opens

CT= CASE TYPE
CY = CASE NUMBER
FY= FISCAL YEAR

CT-CY-0000

EX: ERC-13-0001

1)Create Variable for number set it to
CaseNum = 0
CaseNum = CaseNum +1

1a) Select max (CaseNum) into a variable
1b) Select Case type into variable
1c) Select Year = CY if todays date is between startdate + endate in Calendar table

Variable = Select Year from CY Table where todays date is between start + end

2 Store in Me.CaseNumber