the data method of vector has some wrong

I use the data method of vector in C++, but I have some problems, the code is in belows:

#include <iostream>
#include <vector>

int main ()
{
  std::vector<int> myvector (5);

  int* p = myvector.data();

  *p = 10;
  ++p;
  *p = 20;
  p[2] = 100;

  std::cout << "myvector contains:";
  for (unsigned i=0; i<myvector.size(); ++i)
    std::cout << ' ' << myvector[i];
  std::cout << '\n';

  return 0;
}

the result is myvector contains: 10 20 0 100 0, but why the result is not myvector contains: 10 20 100 0 0, the first one *p = 10; is 10, the second one ++p;*p = 20; is 20, that's all right, but the third one p[2] = 100; should be 100, but it is 0, why?