Script "if" placement

SOLVED

I have a script that works unless the field "UDF_EXCH_RATE"  is zero. (default value is .000000)

Where do I place the "if" statement to get it to work?

tmpAmt = 0 : tmpExchange = 0

retVal = oBusObj.GetValue("ExtensionAmt",tmpAmt)
retVal = oBusObj.GetValue("UDF_EXCH_RATE",tmpExchange)

tmpForeignAmt = tmpAmt / tmpExchange
retVal = oBusObj.SetValue("UDF_FOREIGN_AMOUNT",tmpForeignAmt)

As always, thanks for your assistance.