Pushing to custom stack class freezing .exe - c++

Question

I'm using a stack class, however every time I push something to the stack, the executable freezes and stops working once the line of code pushing is reached.
Could I please get some help on as to why?
My stack.h:
#ifndef STACK_H
#define STACK_H
#include <cassert>
namespace standard
{
class Stack
{
public:
static const int CAPACITY = 30;
void stack() {used=0;};
void push (const char entry);
void pop();
bool empty() const;
int size() const;
char top() const;
private:
char data[CAPACITY];
int used;
};
}
#endif
My stack.cpp:
#include "stack.h"
namespace standard
{
void Stack::push(const char entry)
{
assert(size() < CAPACITY);
data[used] = entry;
++used;
}
void Stack::pop()
{
assert(!empty());
--used;
}
char Stack::top() const
{
assert(!empty());
return data[used-1];
}
int Stack::size() const
{
return used;
}
bool Stack::empty() const
{
if (size() == 0)
return true;
else
return false;
}
}
My calc.cpp:
#include "stack.h"
#include <iostream>
#include <fstream>
using namespace std;
using namespace standard;
void main()
{
Stack myStack;
ifstream input;
input.open("tests.txt");
if (input.fail())
{
cerr << "Could not open input file." << endl;
exit(0);
}
char i;
input >> i;
cout << i;
myStack.push(i); // This is where things go wrong.
cin.get();
}
Thanks for any help!

Answer 1

It looks like you are not initializing used, you have something that may look like a constructor here but it is not:
void stack() {used=0;};
this is what it should look like:
Stack() { used=0;};
So without a constructor used is going to be some indeterminate value and will probably end up with you attempting to access data way out of bounds. Also main should always return int.

Answer 2

void stack() {used=0;};
should this be capitalised? & remove the void!
Stack myStack;
should this be
Stack myStack = new Stack();
if you don't initialise it, the variable myStack will be a "null pointer".

Answer 3

I think you wrote this function wrong:
void stack() {used=0;};
//^^extra ; here
should be
Stack() {used = 0;}
//^^Note that constructor has no return type
You have never really used the stack member function which return void. This results in the fact that used was never initialized. You probably mean the constructor of Stack. Meanwhile, you should use constructor initialization list:
Stack(): used(0) {}