Vector Pointer weird result

I just write a code to copy a vector value of another vector and when I edit the second vector the original one should be impact so here the code there is something that I don't understand :

#include <iostream>
#include <string>
#include <vector>
using namespace std;
int main()
{
  vector<int>a={1,2,3,4,5};
  vector<int>*b=new vector<int>(6);
  b=&a;
  (*b).push_back(7);
  for(int i=0;i<=6;i++){
      cout<<a[i];
      }
      cout<<endl;
   for(int i=0;i<=6;i++){
      cout<<(*b).at(i);
      }

delete b; } the question is why I get this result when I run the program: 1234570 123457 why I dont get the last zero in both of them and thanx~