Simple bank chech spreadsheet help

I have a spreadsheet to keep check on bank account and need help with a formula. =sum(E1+D2-C2) This is in line 2, E1 is opening balance on line 1, it works but when I copy to rest of E column I get running balance in every unused row, is it possible to make empty rows show 0 or nothing until something entered in columns C or D. Helpfrom you younger brainy users appreciated.

Duplicate thread closed - one thread per issue only, please.