std::vector<int>::iterator it;
// /cut/ search for something in vector and point iterator at it.
if(!it) //check whether found
    do_something();

std::vector<int>::iterator i = std::find(v.begin(), v.end(), 13);
if (i != v.end())
{
     // ...
}

if(it != aVector.end())  //past-the-end iterator
    do_something();