What was the most dangerous programming mistake you have made in C?

Question

I am an intermediate C programmer. If you have made any coding mistake that you came to know later that it was the most hazardous / harmful to the total application please share

Answer 1

It has been a long time, but some things you never forget ;-).

• forget the \0 at the end of a string.
• allocate n characters for a string with n characters.
• forgetting the break in a switch statement.
• 'creative' macro use.