Program crashes despite no logical errors [closed] - c++

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I'm basically trying to reverse the stack by passing it to a function. However, the program just crashes when I run it and I can find no logical errors as I have even overloaded the assignment operator to deal with pointer data members.
#include <iostream>
using namespace std;
/***************************************************************************/
class AStack {
public:
AStack();
AStack(int);
~AStack();
AStack operator = (AStack s);
void push(int);
int pop();
int top();
bool isEmpty();
void flush();
private:
int capacity;
int* a;
int index = -1; // Index of the top most element
};
AStack::AStack() {
a = new int[25];
capacity = 25;
}
AStack::AStack(int size) {
a = new int[size];
capacity = size;
}
AStack::~AStack() {
delete[] a;
}
AStack AStack::operator = (AStack s) {
capacity = s.capacity;
int* a = new int[capacity];
for (int i = 0; i < capacity; i++) {
a[i] = s.a[i];
}
index = s.index;
return *this;
}
void AStack::push(int x) {
if (index == capacity - 1) {
cout << "\n\nThe stack is full. Couldn't insert " << x << "\n\n";
return;
}
a[++index] = x;
}
int AStack::pop() {
if (index == -1) {
cout << "\n\nNo elements to pop\n\n";
return -1;
}
return a[index--];
}
int AStack::top() {
if (index == -1) {
cout << "\n\nNo elements in the Stack\n\n";
return -1;
}
return a[index];
}
bool AStack::isEmpty() {
return (index == -1);
}
void AStack::flush() {
if (index == -1) {
cout << "\n\nNo elements in the Stack to flush\n\n";
return;
}
cout << "\n\nFlushing the Stack: ";
while (index != -1) {
cout << a[index--] << " ";
}
cout << endl << endl;
}
/***************************************************************************/
void reverseStack(AStack& s1) {
AStack s2;
while (!s1.isEmpty()) {
s2.push(s1.pop());
}
s1 = s2;
}
/***************************************************************************/
int main() {
AStack s1;
s1.push(1);
s1.push(2);
s1.push(3);
s1.push(4);
s1.push(5);
reverseStack(s1);
cout << "\n\nFlushing s1:\n";
s1.flush();
system("pause");
return 0;
}

Answer 1

You are not providing a copy-constructor, and your assignment operator takes the argument by value. The statement s1 = s2 creates a copy of s2 by calling the implicitly defined copy constructor that copies the pointer, then assigns to s1. At the end of the expression the copy is destroyed, calling delete [] on the pointer. At the end of the function the destructor for s2 runs and attempts to delete [] the same pointer again.
You need to provide a copy constructor that does the right thing.