newb needs help

I apologize if i am posting in the wrong forum for this question in advance - am a rookie to this.

I hardly ever find a need to use Excel, however I was asked to create a spreadsheet that will help us do our monthly narcotic inventory. (Pharmacists)

All goes well until I try to do a SUMIF formula - what I am trying to do is write a formula that says

IF CELL xxx IS BLANK - DO NOTHING BUT IF CELL HAS A NUMBER GREATER THAN ZERO IN IT SUBTRACT THIS CELL FROM CELL yyy AND PUT THE ANSWER HERE

HOPE THIS MAKES SOME SENSE TO THOSE BETTER EDUCATED IN THIS

I TRIED =SUMIF(K5">0",F5-K5) to show an example - in this formula I am trying to put the answer in cell G5

all I am trying to do is have the sheet calculate

Number of Demerol we have to account for eg. 500
Subtract the actual amount we have on hand 200

Getting an answer that would equal the amount dispensed 300

it seems so simple - but if the number that is "on hand" is either zero or blank I get a #VALUE error, and it makes the worksheet look like crap when I print it.

my email is [email protected] if you can help and dont want to post here

thanks

instead of:

=SUMIF(K5">0",F5-K5)

try

=if(k5>0,F5-K5,"")

Also my father in law is a pharmacist and I do all kinds of pharmacist spread sheets, not to mention others... so feel free to email me with any questions anytime.

-eric

[email protected]