Understanding this code involving pointers, arrays, and the new operator - c++

Question

So this is the original code:
class IntegerArray {
public:
int *data;
int size;
};
int main() {
IntegerArray arr;
arr.size = 2;
arr.data = new int[arr.size];
arr.data[0] = 4; arr.data[1] = 5;
delete[] a.data;
}
After moving arr.data = new int[arr.size] to a constructor, it becomes
class IntegerArray {
public:
int *data;
int size;
IntegerArray(int size) {
data = new int[size];
this->size = size;
}
};
int main() {
IntegerArray arr(2);
arr.data[0] = 4; arr.data[1] = 5;
delete[] arr.data;
}
I'm fairly lost on what the code is trying to do. For
IntegerArray(int size) {
data = new int[size];
this->size = size;
}
Is int size just the same as the int size that was declared in the class IntegerArray?
Does data = new int[size] just tell us that data is pointing to the output of the array at int size, with new saying that the size of the array is variable?
Is this-> size = size just a pointer that tells us that the size value of the constructor is just equal to the size parameter of the class?
Why are arr.data[0] and arr.data[1] even mentioned after IntegerArray arr(2)? They don't seem to follow the constructor, but I'm probably just too tired to comprehend that part.

Answer 1

IntegerArray(int size) {
data = new int[size];
this->size = size;
}
Is int size just the same as ...
This int size:
IntegerArray(int size) {
^^^^^^^^
is an argument to the constructor
Does data = new int[size] just tell us ...
new int[size] dynamically allocates an array that contains size number of int objects. data pointer is then assigned to point to that newly created array.
Is this-> size = size just a pointer ...
No. this is a special pointer, that within the constructor points to the object that is being constructed. this->size is the member variable that was declared here:
class IntegerArray {
public:
int *data;
int size;
^^^^^^^^
The complete expression this->size = size assigns the value size that is the constructor argument, to the member variable size.
Why are arr.data[0] and arr.data[1] even mentioned after IntegerArray arr(2)?
The constructor does not initialize the contents of the array (the integer objects within the array). The mentioned code does assigns a values to them.

Answer 2

this->size = size //the fist size is your member variable which is inside IntegerArray. the 2nd size is the size you give over to the Method
data = new int[size]; // here you are creating a new array with the size of "size"
the method IntegerArray(int size) is a constructor method, you only can call it once per object (even at the time when you create the object)
int main() //the startpoint of your program
{
IntegerArray arr(2); //you are creating a new object with a size of 2
arr.data[0] = 4; arr.data[1] = 5; //because of your array is public, you can call it direct from outside (you sould define it as private ore protected). arr.data[0] is the first item of the array, arr.data[1] is the 2nd item
delete[] arr.data;
}
delete[] arr.data; should be inside the destructor of your class...