Those are 4 typical errors I introduced in my code, and spend some time debugging it, because I found them really hard to spot. Luckily, once I spotted the actual bug, I find it a lot easier the next time the typo occurs. Therefore I want to share those, so that I may save you some minutes of your life hunting stupid bugs.

His three contributions concern a "missing if", the addition of a random semicolon, operator precedence and a for loop that refuses to work. Others have contributed to the comments on the post as well.