Excel formula that automatically updates needed?

Question

I need an excel formula to calculate the sum of adjacent cells across columns such that C1=A1+A2, C2=A2+B2 etc. Excel updates my formula for each row when i apply it to a specific range(say C1 to C5). I need excel to automatically apply the formula in accord with the number of data entries so that if i enter data for A1:B5 the formula applies from C1:C5. My problem is that i don't know how many data entries i may need and would like to create a standard sheet where i can enter data in a range without having to worry about applying the formula across the output range each time depending on number data entries. Perhaps a UDF would work?

Answer 1

if I understand this correctly you want excel to automatically put in a formula to add up some cells based on how many cells in a range you might enter?  Don't take this the wrong way, but Excel is a spreadsheet, not mind reading software.  There's now way to tell excel "if I happen to put some numbers in some cells, add them up for me without me doing anything to make it happen".  

just create a simple =SUM(A1:A10) (or whatever the range is) and copy/paste it down as far as you need it to go.  It only takes about 5 seconds to hit <ctrl>C, scroll down while holding the <shift key> and then press <ctrl>V.  

sorry...I know it's not the answer you were looking for but excel can only do so much.