To insert an insert an element in the middle of
a vector, you must add a new element at the end of the vector and
move all elements above the insertion location up by one
slot.
void insert(vector<string>& v int pos, string s)
{
int last = v.size() - 1;
v.push_back(v[last]);
for (int i = last; i > pos; i--)
v[i] = v[i - 1];
v[pos] = s;
}
Note that when you insert an element you start
at the end of the vector, move that element up, then go to the one
before that.