dynamic array cpp

                                    new T[size]

                                    int length = 69;
int * numbers = new int[length];
delete[] numbers;

                                    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.

                                    #include <iostream>
#include <cstddef> // std::size_t
 
int main()
{
    std::cout << "Enter a positive integer: ";
    std::size_t length{};
    std::cin >> length;
 
    int *array{ new int[length]{} }; // use array new.  Note that length does not need to be constant!
 
    std::cout << "I just allocated an array of integers of length " << length << '\n';
 
    array[0] = 5; // set element 0 to value 5
 
    delete[] array; // use array delete to deallocate array
 
    // we don't need to set array to nullptr/0 here because it's going to go out of scope immediately after this anyway
 
    return 0;
}

                                    int main()
{
  int size;

  std::cin >> size;

  int *array = new int[size];

  delete [] array;

  return 0;
}