Can someone help me in pointer in c++

Question

#include <iostream>
using namespace std;

int main() {

// create an array
int num[4] = {3, 6, 9, 12};
// create a pointer variable
int *ptr;

cout << "Array Elements: ";

// loop through array using ptr
for (ptr = num; ptr <= &num[3]; ++ptr) {
cout << *ptr << " ";
}

return 0;
}

// Array Elements: 3 6 9 12

Please explain for loop