/in/foo.c: In function 'main':
/in/foo.c:24:11: error: 'v' undeclared (first use in this function)
  if (d == v) {
           ^
/in/foo.c:24:11: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:23:12: warning: unused variable 'mid' [-Wunused-variable]
  const int mid = high + low / 2;
            ^~~