With -std=c89 you shouldn't need that `int k`, right? Further, you can add includes on the command line cc -std=c89 donut.c -include stdio.h -include stri

With -std=c89 you shouldn't need that `int k`, right? Further, you can add includes on the command line cc -std=c89 donut.c -include stdio.h -include string.h -include math.h -lm Then the source can be left as is.