assert() is a macro that will print an error message and abort the program if its argument doesn't evaluate to true. assert() is usually used in debug builds t

assert() is a macro that will print an error message and abort the program if its argument doesn't evaluate to true. assert() is usually used in debug builds to verify internal invariants of the code: "if this is false, something has gone horribly, terribly wrong; we've gone crazy and we should abort to avoid further hurting ourselves or others". It shouldn't be used to verify that user input is well-formed, since this happens under normal circumstances.