foo.cc: In function ‘int main()’:
foo.cc:6:22: warning: ‘n’ is used uninitialized [-Wuninitialized]
    6 |         for(int i=1;i<=n;i++)
      |                     ~^~~
foo.cc:5:13: note: ‘n’ was declared here
    5 |         int n,sum=0;
      |             ^