Jump

Until a program has a jump in it, it runs top to bottom and, on reaching the end, starts from the top again — doing the same thing whatever the circumstances. jump is the instruction that changes that: one check, and execution goes off to the side. Writing to @counter does the same job, but that is used rarely and deliberately.

The line is built like this: where to jump, which condition and what to compare with what. If the condition holds, the next line to run is the one the arrow points at; if not, the ordinary next one.

Everything else is assembled from that:

• a branch — a jump forward, over a piece of the program;
• a loop — a jump backwards, to a line that has already run.

To the processor there is no difference between them: in both cases the number of the next line simply changes. That is why there are only three lessons.

Lessons

1. Condition and branchingOne check — two roads. How a program stops being a straight line
2. LoopsThe same jump, only the arrow points up — and the program starts repeating a piece of itself
3. Nested conditions and early exitA jump has one condition and one target. Everything else — «and», «or», else, leaving a loop — is assembled out of several jumps

What you need first

«How the processor works» — that a program runs in an endless loop, and what @counter is. The comparisons are the same as op’s, so «Comparisons and logic» will come in handy, though it is not required.