How do you create an object on the heap in C++?

Use new: Vehicle *v = new Vehicle(4); — it returns a pointer you must later free with delete v;.

* Stack objects clean themselves up at scope end; heap objects live until you delete them yourself — miss it and you leak. *

int main() {
    Vehicle *v = new Vehicle(4);   // allocate on the heap
    v->show();                     // arrow notation for pointer access
    delete v;                      // free the memory (and run the destructor)
    return 0;
}

Key differences from stack allocation:

Tip: Every new needs a matching delete, or you leak memory. In modern C++, prefer smart pointers (unique_ptr, shared_ptr) which delete for you automatically.

Go deeper:

• new expression — cppreference — what new really does: allocate, then construct.
• new and delete — Wikipedia — the allocation pair explained with examples.