/in/foo.cc: In function 'int main()':
/in/foo.cc:54:25: error: 'cin' was not declared in this scope
  for(int i=1;i<=na;++i) cin>>A[i];
                         ^~~
/in/foo.cc:55:25: error: 'cin' was not declared in this scope
  for(int i=1;i<=nb;++i) cin>>B[i];
                         ^~~