declare dynamic array c++

int main()
{
  int size;

  std::cin >> size;

  int *array = new int[size];

  delete [] array;

  return 0;
}

int* a = NULL;   // Pointer to int, initialize to nothing.
int n;           // Size needed for array
cin >> n;        // Read in the size
a = new int[n];  // Allocate n ints and save ptr in a.
for (int i=0; i<n; i++) {
    a[i] = 0;    // Initialize all elements to zero.
}
. . .  // Use a as a normal array
delete [] a;  // When done, free memory pointed to by a.
a = NULL;     // Clear a to prevent using invalid memory reference.

int length = 50;
int *array = new int[length]();
// returns 50 length array of 0