Decisions

What this is

A greeting can already use different input to produce different output while following the same instructions. Here we choose which instructions run: ask a question and take a path according to its answer.

Four units take that from a single test to a chain of them, to keeping an answer in a box for later, to joining questions so one test can ask about several things at once.

Who it’s for

You will use stored values and compare numbers: less than, greater than and equal to. We explain each test as it appears. The Basics and Working It Out offer more practice; prior attendance is not required. BASIC and assembly remain independent entry points.

The shape

• Making a choice — IF, and the questions =, < and >.
• One or the other — ELSE, and a chain of questions with one answer.
• A yes you can keep — TRUE and FALSE as values, and the flag that carries an answer from where it was found to where it is needed.
• Asking two things at once — AND, OR and NOT, and brackets that say what to work out first.

Next comes Repeating. If your tests are getting tangled, Truth Tables is a short side-path from here that shows you how to be sure what a test does.