foo.cc: In function 'int main()':
foo.cc:10:28: warning: 'sum' may be used uninitialized [-Wmaybe-uninitialized]
   10 |                         sum+=i;
      |                         ~~~^~~
foo.cc:5:19: note: 'sum' was declared here
    5 |         int     n,sum;
      |                   ^~~