c++ - passing a vector member (struct) to a function

Question

I am getting errors on following lines of code.I am trying to pass vector p's element p[0],p[1],p[2],p[3] to the function distance.

typedef struct {
     long long x,y;
} point; 

long long distance (point A,point B)
{
    int d1 = A.x - B.x ;
    int d2 = A.y - B.y ;
    long long d = d1 * d1 + d2 *d2 ;
    return d ;
}

 //in main function I declared vector <point> p and took input and then,
    x1 = distance (p[0],p[1]) ; // this line is causing error
    x2 = distance (p[1],p[2]) ; // this line is causing error
    x3 = distance (p[2],p[3]) ; // this line is causing error
    x4 = distance (p[3],p[0]) ; // this line is causing error

errors generated :

In file included from /usr/include/c++/4.6/bits/stl_algobase.h:66:0,
                 from /usr/include/c++/4.6/bits/char_traits.h:41,
                 from /usr/include/c++/4.6/ios:41,
                 from /usr/include/c++/4.6/ostream:40,
                 from /usr/include/c++/4.6/iostream:40,
                 from d.cpp:19:
/usr/include/c++/4.6/bits/stl_iterator_base_types.h: In instantiation of ‘std::iterator_traits<point>’:
d.cpp:83:27:   instantiated from here
/usr/include/c++/4.6/bits/stl_iterator_base_types.h:166:53: error: no type named ‘iterator_category’ in ‘struct point’
/usr/include/c++/4.6/bits/stl_iterator_base_types.h:167:53: error: no type named ‘value_type’ in ‘struct point’
/usr/include/c++/4.6/bits/stl_iterator_base_types.h:168:53: error: no type named ‘difference_type’ in ‘struct point’
/usr/include/c++/4.6/bits/stl_iterator_base_types.h:169:53: error: no type named ‘pointer’ in ‘struct point’
/usr/include/c++/4.6/bits/stl_iterator_base_types.h:170:53: error: no type named ‘reference’ in ‘struct point’

Help is needed.