foo.cc: In function ‘int main()’:
foo.cc:10:4: warning: ‘sum’ may be used uninitialized [-Wmaybe-uninitialized]
   10 | sum=sum+a;
      | ~~~^~~~~~
foo.cc:5:17: note: ‘sum’ was declared here
    5 | long long a=1,x,sum;
      |                 ^~~