This macro finds values of zero in numeric fields and changes them to null. It illustrates how to read records in a dataview, get values for some or all of the fields in a record, check and change values in fields, and write updated values back to the fields.
You can read just the records in a selection set and/or visit the records in sort order using different values for the arguments for GetFirstRecord() and GetNextRecord(). You can choose which fields to read or write by building fields_arrays and values_array in different ways. You can fill fields based on the results of expressions. Consider this macro to be a shell that you can adapt to many different tasks.