Linked List Stack Problem Postop

[whoShmurf]

Hi, I'm having trouble getting my linked list to work properly. There seems to be a memory access violation. Also, for the "show" function, how would I get it to output the stack starting at the bottom? Would I need to add a "Node * bottom" pointer to keep track of that? Any help would be much appreciated.

#include <iostream>
#include <cmath>
#include <sstream>
using namespace std;

struct Node{
	double data;
	Node * next;
};

class Stack{
public:

	Stack();
	~Stack();
	unsigned size() const;
	void push(double item);
	double pop();
	double top() const;

	void show()const;

private:
	Node * sTop;
};

bool calculate(double & result);

bool die(const string & msg);

int main(){

	/*
	double result;

	calculate(result) ? cout << '\t' << result : cout << '\t' << "bogus";
	cout << endl << "bye" << endl;
	*/



	Stack test;
	double Top;
	unsigned Size;
	test.push(0);
	test.push(1);
	test.push(2);
	test.show();
	Top = test.top();
	cout << "Top: " << Top << endl;
	Size = test.size();
	cout << "Size: " << Size << endl;

	
	test.pop();
	test.pop();
	Top = test.top();
	test.show();
	cout << "Top: " << Top << endl;
	Size = test.size();
	cout << "Size: " << Size << endl;


	test.push(1);
	test.push(2);
	test.push(3);
	test.push(4);
	test.show();
	Top = test.top();
	cout << "Top: " << Top << endl;
	Size = test.size();
	cout << "Size: " << Size << endl;

	
	return 0;
}

Stack::Stack(){

	sTop = NULL;
}

Stack :: ~Stack(){

	while (sTop){
		pop();
	}

}

unsigned Stack::size() const{

	unsigned size = 0;

	for (Node * temp = sTop; temp != NULL; temp = temp->next){
		size++;
	}

	return size;

}

double Stack::top() const{

	double temp;

	if (!sTop ){
		die("Stack underflow");
	}

	Node * tempPtr = sTop;

	
	temp = tempPtr->data;
	tempPtr = tempPtr->next;
	

	return temp;
}

void Stack::push(double item){

	Node * newData = NULL;

	try{

		newData = new Node;
	}
	catch (const bad_alloc &){

		die("Memory allocation failed");
	}

	newData->data = item;
	newData->next = sTop;
	sTop = newData;

}

double Stack::pop(){

	if (!sTop){

		die("Stack underflow");
	}

	double tempVal;
	Node * oldData = sTop;
	sTop = oldData->next;
	tempVal = oldData->data;
	delete oldData;

	return tempVal;

}

void Stack::show()const{

	cout << "Stack Elements:";


	unsigned x = size();
	x = x - 1;

	for (Node * temp = sTop; temp != NULL; temp = temp->next){

		cout << " [" << x << "]: " << temp->data;
		x--;
	}

	cout << endl;
}



bool die(const string & msg){

	cout << "Error: " << msg << "The program will now exit." << endl;
	exit(EXIT_FAILURE);
}


bool calculate(double & result){

	Stack test;

	char type;
	cin >> type;

	while (type != '.'){



		if (type == '#'){
			double number;
			cin >> number;
			test.push(number);
		}
		else if (type == '!'){

			char op;
			cin >> op;

			double left, right, value;

			if (op == '+'){
				right = test.pop();
				left = test.pop();
				value = left + right;
				test.push(value);
			}

			if (op == '-'){
				right = test.pop();
				left = test.pop();
				value = left - right;
				test.push(value);
			}

			if (op == '*'){
				right = test.pop();
				left = test.pop();
				value = left * right;
				test.push(value);
			}

			if (op == '/'){
				right = test.pop();
				left = test.pop();
				value = left / right;
				test.push(value);
			}

		}

		cin >> type;


	}

	if (test.size() != 1){
		return false;
	}

	result = test.pop();
	return true;

}

[cire]

There seems to be a memory access violation.

I don't see anything obvious.

Also, for the "show" function, how would I get it to output the stack starting at the bottom? Would I need to add a "Node * bottom" pointer to keep track of that?

No, that wouldn't help. The problem is that you can only navigate your linked list one way and that is from top to bottom, so you need to remember previous nodes somehow. That kind of lends itself naturally to recursion:

unsigned show(const Node* node)  { // helper function
    unsigned index = 0;

    if (node == nullptr)
        return index;

    // show the next node before...
    if (node->next)
        index = show(node->next);

    // showing this one
    std::cout << " [" << index << "]: " << node->data;
    return index + 1;
}


void Stack::show()const {
 
    cout << "Stack Elements:";
    ::show(sTop);
    std::cout << '\n';
}

Your top method is wrong.