/in/foo.cc: In function 'int main()':
/in/foo.cc:11:2: warning: 'i' may be used uninitialized in this function [-Wmaybe-uninitialized]
  if (num==x) return 1;
  ^~
/in/foo.cc:18:10: note: 'i' was declared here
  for(int i;i<=x;i++)
          ^