Write a dynamic array - c++

Question

I want to write a program that can use a dynamic array.
A size is to be passed via the constructor and as soon as this size is reached, a new array is generated in which the previous values are copied into it.
For this, I overloaded the [] operator. The program seems to work at first glance.
But after I tried to implement an array with the size 100 and to save 20000 elements here, different numbers are output.
At the first run, more than 7000 numbers were displayed. After another run over 1800. However, never the desired 20000.
What could be the reason for this?
#include <iostream>
using namespace std;
template<class T>
class Container{
public:
T *dynamicArray;
private:
T *newArray;
int size;
public:
Container(int size){
this->size=size;
dynamicArray=new T[size];
}
T operator[] (unsigned long index){
if(index>size-1){
newArray=new T[size+(index-size)];
T i;
for(i=0; i<(size+(index-size)); i++){
newArray[i]=dynamicArray[i];
}
delete[] dynamicArray;
dynamicArray=newArray;
delete[] newArray;
}
return dynamicArray[index];
}
};
int main()
{
Container <int> dArray(100);
for(int i=1; i<20000; i++){
dArray.dynamicArray[i]=i;
cout << dArray.dynamicArray[i] << "\n";
}
return 0;
}
Thank you!

Answer 1

first , this code didn't call the overloaded [] operator function , its just using default operator [] of type T array , and it never allocate any memory , you can output at allocate memory position
dArray.dynamischesArray[i]=i;
cout << dArray.dynamischesArray[i] << "\n";
and there it some error logic in the overloaded [] operator function
T operator[] (unsigned long index){
if(index>size-1){
neuesArray=new T[size+(index-size)];
T i;
for(i=0; i<(size+(index-size)); i++){
neuesArray[i]=dynamischesArray[i];
}
delete[] dynamischesArray;
dynamischesArray=neuesArray;
//delete[] neuesArray; cannot deleted ,course error
size = index + 1; //keep size sync real size
}
return dynamischesArray[index];
}
this is modified code can be run correct :
#include <iostream>
#include <string>
using namespace std;
template<class T>
class Container {
public:
T *dynamischesArray;
private:
T *neuesArray;
int size;
public:
Container(int size) {
this->size = size;
dynamischesArray = new T[size];
}
T& operator[] (unsigned long index) {
if (index > size - 1) {
cout << "allocate :" << index<<"\n";
neuesArray = new T[index+1];
unsigned long i;
for (i = 0; i < size; i++) {
neuesArray[i] = dynamischesArray[i];
}
delete[] dynamischesArray;
dynamischesArray = neuesArray;
//delete[] neuesArray;
size = index+1;
}
T&ret = dynamischesArray[index];
//return dynamischesArray[index];
return ret;
}
};
int main()
{
Container <int> dArray(100);
for (int i = 1; i < 20000; i++) {
dArray[i] = i;
cout <<"i="<<i<<" "<< dArray[i] << "\n";
//dArray.dynamischesArray[i] = i;
//cout << dArray.dynamischesArray[i] << "\n";
}
return 0;
}
this is result