Passing a vector as argument and using it, why does it crash?

I'm fairly new to C++ especially STL. I'm trying to pass a vector as argument to a function, but it causes the application to crash. I'm using Code::Blocks and MingW. Here is a simple code.

#include <iostream>
#include <vector>

using namespace std;

void foo(const vector<int> &v)
{
    cout << v[0];
}
int main(){
    vector<int> v;
    v[0] = 25;
    foo(v);
return 0;
}

Thanks!