StackList.cpp

// C++ code
#include <iostream>
class StackList;

class StackNode{
private:
    int data;
    StackNode *next;
public:
    StackNode():data(0){
        next = 0;
    }
    StackNode(int x):data(x){
        next = 0;
    }
    StackNode(int x, StackNode *nextNode):data(x),next(nextNode){};
    friend class StackList;
};

class StackList{
private:
    StackNode *top;     // remember the address of top element 
    int size;           // number of elements in Stack
public:                 
    StackList():size(0),top(0){};
    void Push(int x);
    void Pop();
    bool IsEmpty();
    int Top();
    int getSize();
};

void StackList::Push(int x){

    if (IsEmpty()) {
        top = new StackNode(x);
        size++;
        return;
    }

    StackNode *newnode = new StackNode(x);  // Push_front() in Linked list
    newnode->next = top;                    
//    StackNode *newnode = new StackNode(x,top);
    top = newnode;
    size++;
}

void StackList::Pop(){

    if (IsEmpty()) {
        std::cout << "Stack is empty.\n";
        return;
    }

    StackNode *deletenode = top;
    top = top->next;
    delete deletenode;
    deletenode = 0;
    size--;
}

bool StackList::IsEmpty(){

    return (size == 0);     // if size==0, return true
}

int StackList::Top(){

    if (IsEmpty()) {
        std::cout << "Stack is empty.\n";
        return -1;
    }
    return top->data;
}

int StackList::getSize(){

    return size;
}

int main(){

    StackList s;
    s.Pop();
    s.Push(32);
    s.Push(4);
    std::cout << "\ntop: " << s.Top() << "\nsize: " << s.getSize() << std::endl;        
    s.Push(15);
    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;
}