/in/foo.cc: In function 'int main()':
/in/foo.cc:7:7: warning: unused variable 'flag' [-Wunused-variable]
  bool flag=0;
       ^~~~
/in/foo.cc:24:10: warning: 'sign' may be used uninitialized in this function [-Wmaybe-uninitialized]
   a[sign]=b[m];
   ~~~~~~~^~~~~