I am getting a issue in copying a pointer to another pointer in c++

I am getting segmentation fault in first code but the second code is running fine, don't know how?

#include <iostream>

using namespace std;

int main() {
    int *p;
    int *p1;
    *p1=7;
    p=p1;
    cout<<*p<<" "<<p;
    return 0;
}

#include <iostream>

using namespace std;

int main() {
    int *p1;
    *p1=7;
    int *p=p1;
    cout<<*p<<" "<<p;
    return 0;
}    
//7 0x7ffeea73db70