/in/foo.cc: In function 'int main()':
/in/foo.cc:9:22: error: 'a' was not declared in this scope
    9 |                 cin>>a;
      |                      ^
/in/foo.cc:10:21: warning: unused variable 'sum' [-Wunused-variable]
   10 |                 int sum=0;
      |                     ^~~