試題詳解

4. The ADT stack can be defined by the following axioms:
(aStack.createStack()).isEmpty() = true
(aStack.push(item)).isEmpty() = false
(aStack.createStack()).pop() = error
(aStack.createStack()).getTop() = error
(aStack.push(item)).getTop() = item
(aStack.push(item)).pop() = aStack
For the following expression:
(((((((aStack.createStack()).push(1)).push(2)).pop()).push(3)).pop()).pop()).isEmpty()
what is the value returned?
(A) an item；
(B) a stack；
(C) true；
(D) false.