Commodore Calculator for Commodore 64, PET, 128, 16, Plus/4, etc.
This is an example calculator program including operator precedence. Use is like a handheld calculator. Keys are shown on screen. Works in 40 and 80 column screens. A few manual edits to adjust screen use (lines 1-9) and it will work on Vic-20 as well! Only works with integers at this time. It is intended to be upgraded.
Link: blog entry
Instructions
LOAD"CALC64",8
RUN
Use STOP
to quit