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Calculator Program

rmartin20 (21)
I have a c++ book that has given me some code for input and execution for a calculator program. I created a template class for Node and Stack operations for storage and have it working, I think... Anyways I cannot figure out why it's no adding when I am using the program, I think I am just confused on how they implemented the commands..

Stack.h

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#ifndef STACK_H
#define STACK_H

#include <iostream>
#include <new>
#include <cstdlib> 
using namespace std;

#include "Node.h"

template <typename T>
class Stack {
private:
    Node<T>* top;
public:

    class StackEmptyException {
    }; // empty inner typename for exception handling
    Stack();
	char get_command(); 
	bool do_command(char command, Stack<T> &numbers); 
    virtual ~Stack();
    void push(T);
    T pop();
    bool isEmpty();
    bool isFull();
};

// constructor: new stack is created. top is null.

template <typename T>
Stack<T>::Stack() {
    top = NULL;
}

// destructor: free all the memory allocated for the stack

template <typename T>
Stack<T>::~Stack() {
    while (!isEmpty())
        pop();
}

// push a data onto the stack

template <typename T>
void Stack<T>::push(T data) {
    try {
        Node<T>* newNode = new Node<T > (data);
        newNode->setNext(top);
        top = newNode;
    } catch (bad_alloc &e) {
        cout << "memory allocation exception: " << e.what() << endl;
        exit(1);
    }
}

// pop the data from the stack

template <typename T>
T Stack<T>::pop() {
    if (isEmpty())
        throw StackEmptyException();

    T data = top->getData();
    Node<T>* discard = top;
    top = top->getNext();
    delete discard;
    return data;
}

// is stack empty?

template <typename T>
bool Stack<T>::isEmpty() {
    if (top == NULL) return true;
    else return false;
}

// is stack full? 

template <typename T>
bool Stack<T>::isFull() {
    return false; // never, unless memory is full
}
template<typename T>
bool do_command(char command, Stack<T> &numbers) {
	double p,q; 
	switch(command) {
	case '?':
		cout << "Enter a real number: " <<flush;
		cin>>p; 
		if(numbers.isFull()) 
			cout << "Warning: Stck full, lost number" <<endl;
		break; 
	case '=':
		if(numbers.isEmpty())
			cout << "Stack empty" <<endl; 
		else {
			cout << p << endl; 
			break; 
		}
	case '+':
		if(numbers.isEmpty())
			cout << "Stack empty" <<endl; 
		else
		{
			numbers.pop();
			if(numbers.isEmpty()) {
				cout << "Stack has just one entry" <<endl; 
				numbers.push(p); 
			}
			else
			{
				numbers.pop();
				if(numbers.isFull()) 
					cout << "Warning: Stack full, lost result" <<endl;
			}
		}
		break; 
	case 'q':
		cout << "Calculation finished\n";
		return false;
	}
	return true; 
}
char get_command() {
	char command;
	bool waiting = true; 
	cout << "Select command and press <Enter>: ";
	while(waiting) {
		cin >> command;
		command = tolower(command);
		if(command == '?' || command == '=' || command == '+' 
			|| command == '-' || command == '*' || command == '/' 
			|| command == 'q') waiting = false; 
		else
		{
			cout << "Please enter a valid command:" <<endl
			<< "[?]push to stack [=]print top" <<endl
			<< "[+] [-] [*] [/] are arithmetic operations" <<endl 
			<< "[Q]uit." <<endl; 
		}
	}
	return command; 
}

#endif


Node.h

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#ifndef NODE_H
#define NODE_H

template <class T>
class Node {
private:
  T data;
  Node<T>* next;
public:
  Node(T);
  virtual ~Node(); // base class destructor must be virtual
  T getData();
  Node<T>* getNext();
  void setNext(Node<T>*);
  void setData(T d);
};

// constructor: create a new Node with d as data
template <class T>
Node<T>::Node(T d) {
  data = d;
  next = 0;
}

template <class T>
Node<T>::~Node() {
}

// store data
template <class T>
void Node<T>::setData(T data) {
  this->data = data;
}

// set link
template <class T>
void Node<T>::setNext(Node<T>* next) {
  this->next = next;
}

// get next link
template <class T>
Node<T>* Node<T>::getNext() {
  return next;
}

template <class T>
T Node<T>::getData() {
  return data;
}

#endif


main.cpp

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#include "Stack.h"

int main() {
Stack<double> numbers; 

while(do_command(get_command(),numbers));
return 0; 
}
Peter87 (11234)
In case '?' you never call push.
In case '=' you only break if the stack is not empty.
rmartin20 (21)
I added the numbers.push(p); for '?' command, but when I run the program it gives me 0 every time when I use '=' after pushing real numbers.
Peter87 (11234)
In case '=' you print p which is uninitialized.
rmartin20 (21)
that makes sense, my next question is:

if p is the oject that they are using to store and print nodes, for '=' i would want to cout << numbers.top?
rmartin20 (21)
nevermind, I had to look at it a little longer, using cout<<numbers.pop() was the appropriate method
ToniAz (351)
If you're not after learning classes and data structure but rather after the calculator itself, use the STL containers, stack is supported.
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