指针问题求解

#include<iostream>
using namespace std;
int main()
{
    int a[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, };

    int *p = a + 5, *q = NULL;
    q = p + 5;

    cout << *(p+5) << endl;

    cout << *p << " " << *q << endl;

    return 0;

}

为什么*q=*(p+5)就报错呢， 和q=p+5区别没搞懂。。求帮解释下