#include <iostream>

int main() {
    int size;
    std::cout << "How many elements? ";
    std::cin >> size;

    // Allocate dynamic array on heap
    int* arr = new int[size];           // raw allocation – no initialization

    // Fill it (garbage values otherwise!)
    for (int i = 0; i < size; i++) {
        arr[i] = i * 10;
    }

    // Use it
    for (int i = 0; i < size; i++) {
        std::cout << arr[i] << " ";
    }
    std::cout << "\n";

    // MUST delete[] – not delete!
    delete[] arr;                       // wrong: delete arr → undefined behavior
}



The Modern Fix Everyone Should Use
C++


#include <vector>

std::vector<int> arr(size);   // auto allocates, auto deletes, has .size(), bounds-checked in debug

arr.push_back(999);           // grows automatically
std::cout << arr[0] << "\n";  // safe (throws in debug if out of range)