Locksmith: count each digit once

Locksmith asks you to crack a four-digit code in ten guesses. Repeated digits make the scoring worth a closer look: each occurrence can contribute only once.

Nine lessons build the game through seven runnable Sinclair BASIC programs. Begin with an editable guess and visible practice code, compare positions and count occurrences, then use a history of clues to reason about the answer. Hidden random codes, two endings and a title complete the game. Save it to tape and check the fresh-start path in the final lesson.