C99 is not a strict extension, but as stated in its foreword, "this second edition [C99] cancels and replaces the first edition [C90]". For instance, implicit

C99 is not a strict extension, but as stated in its foreword, "this second edition [C99] cancels and replaces the first edition [C90]". For instance, implicit function declarations are allowed in C90 but not in C99.