foo.cc: In function ‘int main()’:
foo.cc:9:20: warning: ‘i’ is used uninitialized [-Wuninitialized]
    9 |         for(int i;i<=n-1;i++)
      |                   ~^~~~~
foo.cc:9:17: note: ‘i’ was declared here
    9 |         for(int i;i<=n-1;i++)
      |                 ^