c++ Using unordered map

unordered_map<string, int> umap;
vector<int> toReturn;
for(unsigned i = 0; i < queries.size(); ++i) {
    if(queries.at(i).at(0) == "add") {
        for(unsigned j = 0; j < queries.at(i).at(1).size(); ++j){
            ++umap[queries.at(i).at(1).substr(0,j+1)];
        }
    } else if(queries.at(i).at(0) == "find") {
        toReturn.push_back(umap[queries.at(i).at(1)]);
    }
}
return toReturn;