Checking Account Running Total?

For my Visual BASIC class we were asked to create a project to compute your checking account balance.Included in the project should be three radio buttons (deposit,check, and service charge), one text box (the amount),and a read only text box which will show the new balance. The balance should be calculated by adding deposits and subtracting checks and service charges; Each of these must return an updated balance. If there is not enough money to cover a check,do not deduct the check amount, but charge a service charge of ten dollars. The problem I have continually run into is keeping a running balance without using do or for loops. Here is a copy of the code i have come up with which will display only what I enter into the amount text box and put it into the balance read only text box; it will not accumulate.

Code:

Private DepositTotalDecimal, CheckTotalDecimal, ServiceChargeTotalDecimal, BalanceDecimal, AmountDecimal As Decimal
Private DepositCountInteger, CheckCountInteger, ServiceChargeCountInteger As Integer
Private Sub PrintButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PrintButton.Click[code]....