10 If an object that has automatic storage duration is not initialized explicitly, its value is
   indeterminate. If an object that has static storage duration is not initialized explicitly,
   then:
   — if it has pointer type, it is initialized to a null pointer;
   — if it has arithmetic type, it is initialized to (positive or unsigned) zero;
   — if it is an aggregate, every member is initialized (recursively) according to these rules;
   — if it is a union, the first named member is initialized (recursively) according to these
       rules.