/in/foo.cc: In function 'int main()':
/in/foo.cc:7:20: warning: for increment expression has no effect [-Wunused-value]
  for(int i;i<=n;2-n+1)
                 ~~~^~
/in/foo.cc:7:13: warning: 'i' may be used uninitialized in this function [-Wmaybe-uninitialized]
  for(int i;i<=n;2-n+1)
            ~^~~
/in/foo.cc:16:24: warning: 'sum2' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<sum1<<endl<<sum2;
                        ^
/in/foo.cc:16:8: warning: 'sum1' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<sum1<<endl<<sum2;
        ^~~~