assert - program verification
void assert(int expression)
Assert is a macro that indicates expression is expected to be true at
this point in the program. It causes an abort(3) with a diagnostic
comment on the standard output when expression is false (0). Compiling
with the cc(1) option -DNDEBUG effectively deletes assert from the
`Assertion "expression" failed: file f line n.' F is the source file and
n the source line number of the assert statement.