Can I make the values of an IF function into equations?

I'm working on a simple budget sheet in Google Sheets, and want to know if I can make the values of an IF function into an equation.

• Column A describes the activity (as in, purchased DVD, received paycheck, etc).
• Column B lists the amount of the activity if it was income; otherwise, it remains blank.
• Column C lists the amount if the activity was an expense; otherwise, it remains blank.
• Column D is my total amount, which takes the total amount in the cell directly above it and either adds to that value with the value in column B, or subtracts from that value with the value in column C. I have to personally input that equation, which is pretty time-consuming.

I was hoping to use column E to be a row that I mark as "Y" if that row was income. Otherwise, I would leave it blank.

Then I wanted to replace the equation in column D with an IF statement that checks if column E has a "Y" in it. If it does, then it performs the addition equation using columns D and B. (And if E is blank, then the equation simply has column C subtracted from column D.)

Say I have the following table:

1. Col. A    || Col. B ||  Col. C || Col D.

1.  Event    || Income || Expense || Total

1. START VAL.||--------||---------|| $100.00 ||
2. Hamburger ||--------||   $10   || =D3-C4  ||
3. Paycheck  ||  $20   ||---------|| =D4+B5  ||

Instead, I'm hoping to add column E so the table looks like this:

1. --Col. A---||-Col. B-||--Col. C-||----Col D.----||-Col. E----||

2. --Event----||Income--||-Expense-||----Total-----||-Is Income?||

3. STARTVAL.  ||--------||---------||-----$100-----||-----------||
4. Hamburger  ||--------||   $10   ||--*FORMULA 1*-||-----------||
5. Paycheck   ||--$20---||---------||--*FORMULA 2*-||-----Y-----||

I thought that the FORMULA 1 would have to look like this:

=IF(E4="Y",(D3+B4),(D3-C4))

Formula 2 would look like this:

=IF(E5="Y",(D4+B5),(D4-C5))

You can see that having to update each cell by 1 depending on if it's income or an expense is inefficient...

I would expect column E to cause the IF function in column D to produce new equations depending on the value in column E, but all I get in Google Sheets is

Formula Parse error