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Problem with dynamic memory

AndroidZ (64)
The following program
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#include <iostream>
#include <stdlib.h>

using namespace std;
class IntStack
{
    int INITIAL_SIZE;
    int i;
    int* st_arr;
public:
    //default constructor
    IntStack() : INITIAL_SIZE(100), st_arr(new int [INITIAL_SIZE]) {}
    //destructor
	~IntStack() { delete [] st_arr;}
    void reset();
    void push(int n);
    void push(int a[], size_t array_size);
    int pop();
    void pop(int a[], size_t n);
    int top();
    int size();
    void double_capacity();
    bool is_full();
    bool is_empty();
    friend IntStack print_stack(IntStack* pstack);
};

IntStack print_stack(IntStack* pstack){
    int stop = 0;
    for (int idx = 100; idx >= 0; idx--){
        if (pstack->st_arr[idx] != 0){
            stop = idx;
            idx = 0;
        }
    }
    //cout << "STOP POINT IS STACK ELEMENT " << stop << "\n"; //DB
    for (int i = 0; i < stop; i++){
        cout << pstack->st_arr[i] << endl;
        //cout << "i: " << i << endl; //DB
    }
}

int main()
{
    IntStack stack;
    stack.reset();

    std::cout << "pushing 11\n";
    stack.push(11);
    std::cout << "is_empty: " << stack.is_empty() << "\n";
    std::cout << "top: " << stack.top() << "\n";
    std::cout << "pop: " << stack.pop() << "\n";
    std::cout << "is_empty: " << stack.is_empty() << "\n";

    std::cout << "pop: " << stack.pop() << "\n"; // this should result in "STACK EMPTY" output, or similar message
    std::cout << "pop: " << stack.pop() << "\n"; // this should result in "STACK EMPTY" output, or similar message
    std::cout << "is_empty: " << stack.is_empty() << "\n";

    std::cout << "pushing 1\n";
    stack.push(1);
    std::cout << "pushing 2\n";
    stack.push(2);
    std::cout << "pushing 3\n";
    stack.push(3);
    std::cout << "pushing 4\n";
    stack.push(4);

    std::cout << "pop: " << stack.pop() << "\n";
    std::cout << "pop: " << stack.pop() << "\n";
    std::cout << "top: " << stack.top() << "\n";
    std::cout << "pop: " << stack.pop() << "\n";

    std::cout << "stack size: " << stack.size() << "\n";

    stack.reset();

    int arr[] = {0, 1, 2, 3, 4};

    stack.push(arr, 5);
    print_stack(&stack);
    stack.pop(arr, 5);

    std::cout << "stack size: " << stack.size() << "\n";

    for(int i = 0; i < 5; ++i)
    {
        std::cout << arr[i] << "\n";
    }

    return 0;

}


int IntStack::top(){
    i--;
    int temp = i;
    i++;
    return st_arr[temp];
}

int IntStack::size(){
    return i;
}

void IntStack::reset(){
    //loop through the stack and set each element to NULL
    for (i = 0; i < INITIAL_SIZE; i++){
        st_arr[i] = NULL;
    }
    i = 0;
}

void IntStack::push(int n){
    //if stack is full, int cannot be pushed, signal error
    if (i == 100){
        cerr << "STACK EMPTY";
    }
    //set current element of stack to pushed int then increment index
    st_arr[i] = n;
    i++;
}

void IntStack::push( int arr[], size_t array_size ){
    for (int idx = 0; idx < array_size; idx++){
        push(arr[idx]);
    }
}

int IntStack::pop(){
    //if stack is empty, int cannot be set to null, signal error
    if (i == 0){
        cerr << "STACK EMPTY\n";
    }
    else
    //decrement to previous stack index then set it to NULL
    --i;
    int temp = st_arr[i];
    st_arr[i] = NULL;
    return temp;
}

void IntStack::pop( int a[], size_t n ){
    i--;
    for (int idx = 0; idx < n; idx++){
            a[idx] = st_arr[i];
            st_arr[i] = NULL;
        if(i>0)i--;
    }
    //for (i = 0; st_arr[i] != NULL; i++);
    //cout << "after popping, i is " << i << "\n"; //DB
}

bool IntStack::is_full(){
    if(i == 100)
        return true;
    else
        return false;
}

bool IntStack::is_empty(){
    if(i != 0)
        return false;
    else
        return true;
}


produces the output:
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pushing 11
is_empty: 0
top: 11
pop: 11
is_empty: 1
STACK EMPTY
pop: 0
STACK EMPTY
pop: 0
is_empty: 1
pushing 1
pushing 2
pushing 3
pushing 4
pop: 4
pop: 3
top: 2
pop: 2
stack size: 1
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stack size: 0
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0


But I want it to behave like this program:
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#include <iostream>
#include <stdlib.h>
using namespace std;

class IntStack{
    static const int INITIAL_SIZE = 100;
    int i;
    int st_arr[INITIAL_SIZE];
public:
    void reset();
    void push(int n);
    void push(int a[], size_t array_size);
    int pop();
    void pop(int a[], size_t n);
    int top();
    int size();
    bool is_full();
    bool is_empty();
    friend IntStack print_stack(IntStack* pstack);
};

IntStack print_stack(IntStack* pstack){
    int stop = 0;
    for (int idx = 100; idx > 0; idx--){
        if (pstack->st_arr[idx] != 0){
            stop = idx;
            idx = 0;
        }
    }
    //cout << "STOP POINT IS STACK ELEMENT " << stop << "\n";
    for (int i = 0; i <= stop; i++){
        cout << pstack->st_arr[i] << endl;
        //cout << "i: " << i << endl;
    }
}
int main()
{
    /*int arr[5] = {1,2,3,4,5};
    IntStack stack;
    stack.reset();
    stack.push(arr, 5);
    print_stack(&stack);
    //cout << "\n";
    //stack.pop(arr, 5);
    //print_stack(&stack);
    return 0;*/
    IntStack stack;
    stack.reset();

    std::cout << "pushing 11\n";
    stack.push(11);
    std::cout << "is_empty: " << stack.is_empty() << "\n";
    std::cout << "top: " << stack.top() << "\n";
    std::cout << "pop: " << stack.pop() << "\n";
    std::cout << "is_empty: " << stack.is_empty() << "\n";

    std::cout << "pop: " << stack.pop() << "\n"; // this should result in "STACK EMPTY" output, or similar message
    std::cout << "pop: " << stack.pop() << "\n"; // this should result in "STACK EMPTY" output, or similar message
    std::cout << "is_empty: " << stack.is_empty() << "\n";

    std::cout << "pushing 1\n";
    stack.push(1);
    std::cout << "pushing 2\n";
    stack.push(2);
    std::cout << "pushing 3\n";
    stack.push(3);
    std::cout << "pushing 4\n";
    stack.push(4);

    std::cout << "pop: " << stack.pop() << "\n";
    std::cout << "pop: " << stack.pop() << "\n";
    std::cout << "top: " << stack.top() << "\n";
    std::cout << "pop: " << stack.pop() << "\n";

    std::cout << "stack size: " << stack.size() << "\n";

    stack.reset();

    int arr[] = {0, 1, 2, 3, 4};

    stack.push(arr, 5);
    print_stack(&stack);
    stack.pop(arr, 5);

    std::cout << "stack size: " << stack.size() << "\n";

    for(int i = 0; i < 5; ++i)
    {
        std::cout << arr[i] << "\n";
    }

    return 0;


}
int IntStack::top(){
    i--;
    int temp = i;
    i++;
    return st_arr[temp];
}

int IntStack::size(){
    return i;
}

void IntStack::reset(){
    //loop through the stack and set each element to NULL
    for (i = 0; i < INITIAL_SIZE; i++){
        st_arr[i] = NULL;
    }
    i = 0;
}

void IntStack::push(int n){
    //if stack is full, int cannot be pushed, signal error
    if (i == 100){
        cerr << "STACK EMPTY";
    }
    //set current element of stack to pushed int then increment index
    st_arr[i] = n;
    i++;
}

void IntStack::push( int arr[], size_t array_size ){
    for (int idx = 0; idx < array_size; idx++){
        push(arr[idx]);
    }
}

int IntStack::pop(){
    //if stack is empty, int cannot be set to null, signal error
    if (i == 0){
        cerr << "STACK EMPTY\n";
    }
    else
    //decrement to previous stack index then set it to NULL
    --i;
    int temp = st_arr[i];
    st_arr[i] = NULL;
    return temp;
}

void IntStack::pop( int a[], size_t n ){
    i--;
    for (int idx = 0; idx < n; idx++){
            a[idx] = st_arr[i];
            st_arr[i] = NULL;
        if(i>0)i--;
    }
    //for (i = 0; st_arr[i] != NULL; i++);
    //cout << "after popping, i is " << i << "\n";
}

bool IntStack::is_full(){
    if(i == 100)
        return true;
    else
        return false;
}

bool IntStack::is_empty(){
    if(i != 0)
        return false;
    else
        return true;
}


and produce this output:
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is_empty: 1
pushing 1
pushing 2
pushing 3
pushing 4
pop: 4
pop: 3
top: 2
pop: 2
stack size: 1
0
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stack size: 0
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1
0


The only difference between the two is the dynamic allocation of the st_arr array in the stack class. Why does this have an effect? I'm assuming I have to dereference something somewhere, but I'm honestly not sure. I'd appreciate any hints.
kbw (9488)
You don't initialise the stack size i.
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