/in/foo.cc: In function 'int main()':
/in/foo.cc:20:6: error: 'i' was not declared in this scope
  for(i=0;i<n-1;i++)
      ^
/in/foo.cc:30:10: error: 'i' was not declared in this scope
  cout<<a[i]<<" "<<a[i+1];
          ^