foo.c: In function ‘main’:
foo.c:18:25: error: ‘ab’ undeclared (first use in this function); did you mean ‘b’?
   18 |         if((b>a&&b<c)||(ab>c&&b<a))
      |                         ^~
      |                         b
foo.c:18:25: note: each undeclared identifier is reported only once for each function it appears in