foo.cc: In function ‘int main()’:
foo.cc:11:20: warning: ‘sum’ may be used uninitialized [-Wmaybe-uninitialized]
   11 |                 sum+=num%10;
      |                 ~~~^~~~~~~~
foo.cc:7:17: note: ‘sum’ was declared here
    7 |         int num,sum;
      |                 ^~~