c++ not validating string input

int main() {
    Population town;
    int population;
    int numBirths, numDeaths;
    string city, intTest;
    bool isValid = true;

    do {
        cout << "Enter name of city: ";
        cin >> city;
        getline(cin, city);
        for (int i = 0; i < city.length(); i++) {
            if (!(isalpha(city[i]))) {
                isValid = false;
            }
            else {
                isValid = true;
                break;
            }
        }
    } while(!isValid);

Its not properly checking to see if the input is a string or not. Not sure whats wrong with the code.