Unable to understand the pointer mechanism - c++

Question

Why is the program below crashing? I tried debugging the code but couldn't understand; I am suspecting that either the program is wrong or the memory to the passed pointer to display function should have been initialized.
#include <iostream>
using namespace std;
int display( int** intarray )
{
int size = 0;
while( size < 10 )
{
*intarray[size] = size;
size++;
}
return size;
}
int main() {
int* intptrarray;
int arraysize = 0;
arraysize = display( &intptrarray );
for ( int indx = 0; indx < arraysize; indx++ )
{
std::cout << intptrarray[indx] << std::endl;
}
return 0;
}

Answer 1

When a pointer is declared, it doesn't point to any specific memory address. To have it point somewhere, you need to allocate memory to it as follows:
#include <iostream>
using namespace std;
int display( int** intarray, int arraysize )
{
int size = 0;
while( size < arraysize )
{
(*intarray)[size] = size;
size++;
}
return size;
}
int main() {
int arraysize = 10;
int* intptrarray = new int[arraysize];
arraysize = display( &intptrarray, arraysize );
for ( int indx = 0; indx < arraysize; indx++ )
{
std::cout << intptrarray[indx] << std::endl;
}
delete[] intptrarray;
return 0;
}
Whenever you allocate memory, you need to remember to deallocate it yourself (delete for a single variable, delete[] for an array).

Answer 2

*intarray[size] should be (*intarray)[size].
However you have not yet allocated any memory either, so in both cases you are causing undefined behaviour by writing through an uninitialized pointer.
A correct way to write this program is:
void display( std::vector<int> &vec )
{
vec.resize(10);
for ( int i = 0; i < 10; ++i )
vec[i] = i;
}
int main()
{
std::vector<int> vec;
display(vec);
for ( int indx = 0; indx < vec.size(); indx++ )
{
std::cout << vec[indx] << std::endl;
}
}
This can be improved by using std::iota and range-based for-loops if you have a modern compiler.