Jagan gave you an example where you clear the temporary variables before creating them.
In many cases, a good place to put the pcr to clear temporary variables is at the beginning of a sub-schema, and the pcr will clear all temporary variables that are created in that sub-schema.
Some other times, when a WT can have many splits and will use a temporary variable during it's processing, it is required to clear the temporary variable after using it (so that it's value is zero when the second occurrence of the WT is processed).