Error with dynamic memory - c++

Question

I am trying to use the dynamic memory method instead of the vector method to add elements. Initially, the maximum size of the dynamic memory is set to 5. However, as soon as I try to increase more than the capacity of the current the dynamic memory, the elements of the 0th or 1st index loss their references.
The program works fine if I do not specify the size of the dynamic memory,
like: dynamic_memory = new int;. I am wondering why they lose their references
with the resize of the dynamic memory to more than the initial capacity.
PS: I am using Code::Block 16.01
Here is my program.
#include <iostream>
#include <cstdlib>
using namespace std;
class DynamicVector
{
public:
DynamicVector();
virtual ~DynamicVector();
void insertElement(int input);
int showCapacity();
int showSize();
void doubleSize(int * dynamic_memory);
friend ostream& operator << (ostream& outs, const DynamicVector obj);
private:
int * dynamic_memory;
int max_count; // this is similar to the capacity of the vector
int current_count; // this is similar to size of a vector
};
DynamicVector::DynamicVector()
{
max_count = 5;
dynamic_memory = new int[max_count];
current_count = 0;
}
DynamicVector::~DynamicVector()
{
delete [] dynamic_memory;
}
int DynamicVector::showCapacity(){
return max_count;
}
void DynamicVector::insertElement(int input)
{
if (current_count >= max_count)
doubleSize(dynamic_memory);
dynamic_memory[current_count] = input;
current_count++;
}
void DynamicVector::doubleSize(int * dynamic_memory){
int * tmp = new int[max_count];
for (int i = 0; i < max_count; i++)
tmp[i] = dynamic_memory[i];
delete [] dynamic_memory;
max_count = max_count * 2;
dynamic_memory = new int[max_count];
for (int i = 0; i < max_count; i++)
dynamic_memory[i] = tmp[i];
delete [] tmp;
}
int DynamicVector::showSize(){
return current_count;
}
ostream& operator <<(ostream& outs, const DynamicVector obj)
{
for (int i = 0; i < obj.current_count; i++)
outs << obj.dynamic_memory[i] << endl;
return outs;
}
int main()
{
DynamicVector v;
int numberOfIntendedElement = 11;
cout << "Previously, the capacity of vector was: " << v.showCapacity() << endl;
for (int i = 0; i < numberOfIntendedElement; i++)
v.insertElement(i);
cout << "The capacity of the new vector is: " << v.showCapacity() << endl;
cout << "The size of the new vector is: " << v.showSize() << endl;
cout << "The values in the dynamic vector are: \n" << v << endl;
return 0;
}
Result:
41107976
42075512
2
3
4
5
6
7
8
9
10

Answer 1

In
void doubleSize(int * dynamic_memory);
the dynamic_memory defined here shadows the member dynamic_memory; for comedic hi-jinks and undefined behaviour.
The local dynamic_memory is re-pointed at the new buffer, but the member dynamic_memory continues to point at the deleted original address after the function exits. This means that all subsequent inserts go into invalid memory, and Crom only knows what will happen after that.
Solution
Pass in nothing and use the member variable. Redefine the function as
void doubleSize();
Other problems are addressed in the comments and need to be fixed.

Answer 2

Thank you all for your valuable comments and suggestions, especially user4581301 for pointing a comedic hijinks and undefined behavior. After I redefined the function as void doubleSize(), it worked fine. Here is my final working code.
#include <iostream>
#include <cstdlib>
using namespace std;
class DynamicVector
{
public:
DynamicVector();
virtual ~DynamicVector();
void insertElement(int input);
int showCapacity();
int showSize();
void doubleSize();
friend ostream& operator << (ostream& outs, const DynamicVector obj);
private:
int * dynamic_memory;
int max_count; // this is similar to the capacity of the vector
int current_count; // this is similar to size of a vector
};
DynamicVector::DynamicVector()
{
max_count = 5;
dynamic_memory = new int[max_count];
current_count = 0;
}
DynamicVector::~DynamicVector()
{
delete [] dynamic_memory;
}
int DynamicVector::showCapacity(){
return max_count;
}
void DynamicVector::insertElement(int input)
{
if (current_count >= max_count)
doubleSize();
dynamic_memory[current_count] = input;
current_count++;
}
void DynamicVector::doubleSize(){
int * tmp = new int[max_count];
for (int i = 0; i < max_count; i++)
tmp[i] = dynamic_memory[i];
delete [] dynamic_memory;
max_count = max_count * 2;
dynamic_memory = new int[max_count];
for (int i = 0; i < max_count/2; i++)
dynamic_memory[i] = tmp[i];
delete [] tmp;
}
int DynamicVector::showSize(){
return current_count;
}
ostream& operator <<(ostream& outs, const DynamicVector obj)
{
for (int i = 0; i < obj.current_count; i++)
outs << obj.dynamic_memory[i] << endl;
return outs;
}
int main()
{
DynamicVector v;
int numberOfIntendedElement = 11;
cout << "Previously, the capacity of vector was: " << v.showCapacity() << endl;
for (int i = 0; i < numberOfIntendedElement; i++)
v.insertElement(i);
cout << "The capacity of the new vector is: " << v.showCapacity() << endl;
cout << "The size of the new vector is: " << v.showSize() << endl;
cout << "The values in the dynamic vector are: \n" << v << endl;
return 0;
}
Output
Previously, the capacity of vector was: 5
The capacity of the new vector is: 20
The size of the new vector is: 11
The values in the dynamic vector are:
0
1
2
3
4
5
6
7
8
9
10