问C++华氏度到摄氏度(反之亦然)循环问题

EN

int main()
{
    int choice;
    cout << "Please Select A Temperature Scale Conversion:\n"<< endl;
    cout << "1. Convert F to C" << endl;
    cout << "2. Convert C to F\n" << endl;
    cout << "Your Choice: ";
    cin >> choice;

    cout << "Starting Temperature: ";
    cin >> start_temp;
    cout << "Ending Temperature: ";
    cin >> end_temp;
    cout << "Temperature Increase: ";
    cin >> temp_incr;

    if (choice == 1) {
        cout << fixed << setprecision(2) << calcFahrenheit(start_temp) << endl;
    } else if (choice == 2) {
        cout << fixed << setprecision(2) << calcCelsius(start_temp) << endl;
    } else {
        cout << "You have entered an invalid option." << endl;
    }

    system("PAUSE");
    return 0;
}

float calcFahrenheit(float start_temp) {
    float f2c;
    f2c = (5.0/9.0) * (start_temp - 32.0);
    return f2c;
}

float calcCelsius(float start_temp) {
    float c2f;
    c2f = (9.0/5.0) * (start_temp + 32.0);
    return c2f;
}