Untitled

#include <vector>
#include <iostream>
using namespace std;

struct xy{
public:
    int x,y;
    xy(int _x, int _y):x(_x),y(_y){}
};

int main(){
    vector<xy> v,w;

    //either you reserve and then assign values
    v.reserve(1);
    v[0]=xy(1,2); //would crash if you don't reserve
    cout<<v[0].x<<" "<<v[0].y<<endl;

    //or you just push_back
    w.push_back(xy(1,2));
    cout<<v[1].x<<" "<<v[1].y<<endl;

    system("pause");
    return 0;
}