Open Source Computing

Week 10

Start with "I'm harvesting credit card numbers and passwords from your site."

Cathedral v Bazaar

About that "given enough eyeballs, all bugs are shallow" thing ....

Discussion of how to explain what a calculator does

• pressing digits: put them into the display
• pressing operator: clear the display, storing it in prev_display
• pressing =: combining prev_display and current display with the operator.

expression evaluation: ~/271/expressions (code should be in pld.cs.luc.edu/courses/271/spr18/demos/expressionsij.zip)

    java expr_eval     (traced version is expr_exp)

    java expr_assign

Notes: pld.cs.luc.edu/courses/271/spr18/mnotes/recursion.html#exprtrees

Demo of command-line expressions

With a calculator interface, things are a little different. Generally, the '(' key clears the display and starts a new subexpression. Operator keys might display the current operator on the screen. The ')' key acts like the '=' key for the current expression, displaying the results so far. galculator takes this approach.

The other alternative is to display the entire expression on the display line. qalculate does this.