C++ program for Stack Template

#include <iostream>
using namespace std;
//Define the stack class, set default stack size to 2
//use a template to define type at later point
template<class T,int size=2>
class stack{
    private: T data[size];
    int stack_ptr;
    public:
    stack(void);
    void push(T x);
    T pop();
};
//constructor function to initialize stack and data
template<class T,int size>
stack<T,size>::stack(void)
{
    int i;
    for(i=0;i<size;i++) data[i]=0;
    stack_ptr=0;
}
//Push data onto stack
template<class T,int size>
void stack<T,size>::push(T x)
{
    if(stack_ptr>=size)
    {
        cout<<"cannot push data: stack full"<<endl;
        return;
    }
    data[stack_ptr++]=x;
    cout<<"Pushed\t" << x << "\tonto the stack"<<endl;
    return;
}
//Pop data from stack
template<class T,int size>
T stack<T,size>::pop()
{
    if(stack_ptr<=0)
    {
        cout<<"cannot pop data: stack empty"<<endl;
        return data[0];
    }
    cout<<"popped\t"<< data[--stack_ptr]<< "\tfrom stack"<<endl;
    return data[stack_ptr];
}
int main()
{
    //create stack of integers
    stack<int,10> s;
    s.push(45);
    s.pop();
    //try to pop an empty stack
    s.pop();
    s.push(56);
    s.push(29);
    s.push(31);
    s.pop();
    s.pop();
    //create stack of doubles
    stack<double,2> d;
    d.push(4.5);
    d.push(5.9);
    //trying to pushing on a full stack
    d.push(7.2);
    d.pop();
    d.pop();
    //trying to pop an empty stack
    d.pop();
    //declaring stack of characters and using default size
    stack<char> c;
    char w;
    c.push('n');
    c.push('l');
    //trying to push on full stack
    c.push('w');
    c.pop();
    //pick up the stack value
    w=c.pop();
    cout<<"Picked the character ***"<< w << "*** which was popped from top"<<endl;
    //trying to pop an empty stack
    c.pop();
    return 0;
}