/in/foo.cc: In function 'int main()':
/in/foo.cc:20:10: error: 'i' was not declared in this scope
  for(    i=0;i<n2;i++){cin>>a2[i];}
          ^
/in/foo.cc:21:10: error: 'i' was not declared in this scope
  for(    i=0;i<n3;i++){cin>>a3[i];}
          ^