Loops & Repetition: The Off-by-One That Shows Up in Every Language
One boundary character decides whether a loop runs the right number of times or stops one short.
The Loops & Repetition set's most common failure isn't an infinite loop -- it's a loop that runs, finishes, and stops one iteration too early or too late, because a boundary comparison used THAN where it needed OR EQUAL TO, or the other way around. It's the same mistake in every language that has a loop, because it's a mistake about the boundary, not about syntax.
Press Run to see what your code does.
That prints 1, 2, 3, 4 -- one short. The loop keeps going while count is LESS THAN 5, so the moment count becomes 5, the condition is false and the loop stops before showing it. LESS OR EQUAL TO 5 fixes it, because now 5 itself still satisfies the condition on the pass that would show it. The reliable way to catch this isn't staring at the comparison operator -- it's tracing the exact value the loop variable holds on its very last pass, and checking by hand whether that value should or shouldn't make it into the loop body one more time.
Everything above runs in this page, on your own machine. There is more of it on the practice pages.