Debugging: Inside the Machine is a free debugging-practice arcade platformer for students preparing for AP Computer Science Principles or AP Computer Science A. You're inside a corrupted machine — find the USB Key, fix the glitches, and escape the firewall before the system collapses.

CSP and CSA modes ship in the same app. Tap once to switch.

— EASY · MED · HARD —
Each difficulty is a different level, with its own glitch tilemap and its own question bank. CSP topics: Selection, Iteration, Functions & Lists. CSA topics: Variables · Strings, Iteration · Loops, Arrays · Recursion. Two bonus levels (K-Pop Demon Hunters, Minecraft) unlock when you've cleared all three difficulties.

— CODE LENS —
Glitches scatter across each level as collectible bugs. When you're in range, the CODE LENS button pulses on screen. Tap it and a real multiple-choice debugging question appears: read the broken code, pick the actual bug from four explanations, and the glitch repairs. Wrong answer? Stability drops 10 percent. Right answer? Stability recovers 5 percent and the level inches closer to stable.

— Real questions, not filler —
Every question is hand-written and scoped to AP exam topics. No random AI hallucinations, no off-curriculum trivia. The pseudocode reference card (CSP) and Java Quick Reference (CSA) are one tap away during any question.

— Built for phones and tablets —
Touch controls only. Bottom-left D-pad to move, big JUMP button on the right, hold for higher jump. Question screens use full-size answer buttons. Designed for landscape phones and tablets.

— Offline, no account, no tracking —
Everything ships in the app. The game makes zero network calls, collects zero analytics, and requires no sign-in.

— More from CS++ —
A "More from CS++" button connects you to the rest of the CS++ family: the AP CSP and AP CSA full-curriculum web apps, the CS++ Java IDE for on-device Java practice, and the free csplusplus.com web resources (curriculum, vocab trainer, practice exams).

For: AP CSP and AP CSA students, CS teachers building exam prep sessions, anyone who likes finding bugs.