manual running totals

[Mack2]

I am creating manual running totals. My variable is not resetting to zero when the next group starts. This is my code
in header section
Numbervar RunningTotal;
RunningTotal:= 0
Detail section
Numbervar RunningTotal;
if {PurchaseLines.QtyReceived} = next({PurchaseLines.QtyReceived})
then RunningTotal
else RunningTotal:= RunningTotal + {PurchaseLines.QtyReceived}
Footer Section
Numbervar RunningTotal;
RunningTotal
When I get to the next group the variable has the values from the previous group

Help Please

 

[dgillz]

Preface each formula with the statement:
WhilePrintingRecords;

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[Mack2]

Thank you, that did make a difference. But the totals are not correct for every group that has the same number of withdrawls. If within the same group the number of withdrawls are the same it does not add the second number. I am trying to sort those numbers by using the group sort expert, but it is not sorting them.
Then code I have tryed
WhilePrintingRecords;
Numbervar RunningTotal;
if {PurchaseLines.QtyReceived} = next({PurchaseLines.QtyReceived})
//if {PurchaseLines.itemnid} = next({PurchaseLines.itemnid})
//and {PurchaseLines.ItemNid} = next({PurchaseLines.ItemNid})
then RunningTotal
else RunningTotal:= RunningTotal + {PurchaseLines.QtyReceived}
I hope this makes sense, it is driving me crazy. Thanks for your help