if cell = 0 or empty go to previous cell value

I have searched and can't seem to find an answer.

I have a spreadsheet that is used to tract a money market acct. So looking for one cell to reference the most current value without each time have to type in the amount twice.

1. want cell "E1"to equal the last entry in this case B7, but when I fill in B8, B9, … B31 it, so if the cell is blank it looks at the next cell until it finds a value

2. is there away for cell "C8" to be blank if nothing is in cell "B8"