StackArray.cpp

// C++ code
#include <iostream>

class StackArray{
private:
    int top;                 // index of top element
    int capacity;            // allocated memory space of array
    int *stack;              // array representing stack
    void DoubleCapacity();   // double the capacity of stack
public:
    StackArray():top(-1),capacity(1){    // constructor
        stack = new int[capacity];       // initial state: top=-1, capacity=1
    }
    void Push(int x);
    void Pop();
    bool IsEmpty();
    int Top();
    int getSize();
};
void StackArray::DoubleCapacity(){

    capacity *= 2;                            // double capacity
    int *newStack = new int[capacity];        // create newStack

    for (int i = 0 ; i < capacity/2; i++) {   // copy element to newStack
        newStack[i] = stack[i];
    }

    delete [] stack;              // release the memory of stack
    stack = newStack;             // redirect stack to newStack
}

void StackArray::Push(int x){

    if (top == capacity - 1) {    // if stack is full, double the capacity
        DoubleCapacity();
    }
    stack[++top] = x;             // update top and put x into stack
}

void StackArray::Pop(){

    if (IsEmpty()) {          // if stack is empty, there is nothing to pop
        std::cout << "Stack is empty.\n";
        return;
    }
    top--;                    // update top
//    stack[top] = 0;         // (*1)
//    stack[top].~T();        // (*2)
}

bool StackArray::IsEmpty(){

    //    if (top == -1) {
    //        return true;
    //    }
    //    else {
    //        return false;
    //    }
    return (top == -1);
}

int StackArray::Top(){

    if (IsEmpty()) {     // check if stack is empty
        std::cout << "Stack is empty.\n";
        return -1;
    }
    return stack[top];   // return the top element
}

int StackArray::getSize(){

    return top+1;        // return the number of elements in stack
}

int main(){

    StackArray s;
    s.Pop();
    s.Push(14);
    s.Push(9);
    std::cout << "\ntop: " << s.Top() << "\nsize: " << s.getSize() << std::endl;
    s.Push(7);
    std::cout << "\ntop: " << s.Top() << "\nsize: " << s.getSize() << std::endl;
    s.Pop();
    s.Pop();
    std::cout << "\ntop: " << s.Top() << "\nsize: " << s.getSize() << std::endl; 
    s.Pop();
    std::cout << "\ntop: " << s.Top() << "\nsize: " << s.getSize() << std::endl;

    return 0;
}