What is the major difference between a vector and a stack?

Question

Both act like a stack. Both have push and pop operations.

Is the difference in some memory layouts?

Answer 1

std::vector has several accessibility and modification operations compared to std::stack. In case of std::stack, you may have to perform operations only in systematic way, where you can push() above the last element or pop() the last element.

std::vector is more flexible in that sense, where it has several operations, where you can insert() in between or erase() in between.

The major point is that, std::stack needs to be provided the underlying container. By default it's std::deque, but it can be std::vector or std::list too.
On other hand, std::vector is guaranteed to be a contiguous array which can be accessed using operator [].

Answer 2

I'm not aware of all the implementation details, but according to this, stack is a container adaptor. It makes sure the underlying container, which can be a vector, list or deque, works as a stack, i.e. only allows push and pop, and not random access.

So, a vector can work as a stack, but a stack cannot work as a vector, because you cannot insert or get an element at a random position.