how to create a 2D vector: first row of string and second row is integer

There are some possibilities.

If you care for the order of the elements:

vector<pair<string, int>> occurrences;

int main(){
    occurrences.push_back( make_pair("this", 2) );
    occurrences.push_back( make_pair("adam", 4) );
    //access: occurrences[0].first or occurrences[0].second
}

---

Otherwise:

map<string, int> occurrences;             //O(logN) insertion and lookup

unordered_map<string, int> occurrences;   //O(1) insertion and lookup

int main(){
    occurrences["this"] = 2;
    occurrences["adam"] = 4;
}

---

If you want something elaborated, you can use struct:

struct occurrence{
    string word;
    int value;
    occurrence(){}
    occurrence(string w, int v){word = w; value = v;}
};

occurrence ocurrences[10];

int main(){
    ocurrences[0] = ocurrence("this", 2);
    ocurrences[1] = ocurrence("adam", 4);
}

I find it most convenient to create a vector of struct ... or, as the case may be, classes. One field is the name; the other is the count. Access by e.g. vector[n].word or vector[n].wordCount. The virtue of this approach is that it's easy to add more fields at any time.