diff --git a/src/Motorradvermietung.cpp b/src/Motorradvermietung.cpp
index 39382a4..82eae40 100644
--- a/src/Motorradvermietung.cpp
+++ b/src/Motorradvermietung.cpp
@@ -64,14 +64,21 @@ auto int_to_string(const unsigned int value, const unsigned int digits = 0) -> s
     return str;
 }
 
+/**
+ * \brief Present a date with day, month and year
+ */
 class date final
 {
 private:
     unsigned short day_;
     unsigned short month_;
     unsigned short year_;
-    int sum_;
+    int day_num_;
 
+    /**
+     * \brief Get the day number from current day/month/year.
+     * \return Number of days
+     */
     int day_number_from_date() const
     {
         const auto month = (month_ + 9) % 12;
@@ -81,16 +88,27 @@ private:
 
 public:
     date(const unsigned short day, const unsigned short month, const unsigned short year) : day_(day), month_(month),
-                                                                                            year_(year)
+                                                                                            year_(year),
+                                                                                            day_num_(
+                                                                                                day_number_from_date())
     {
-        sum_ = day_number_from_date();
     }
 
-    int get_sum() const
+    /**
+     * \brief Get day num of current day/month/year
+     * \return Number of days
+     */
+    int get_day_num() const
     {
-        return sum_;
+        return day_num_;
     }
 
+    /**
+     * \brief Output operator of date formatted as DD.MM.YYYY
+     * \param ostr output stream
+     * \param date current date
+     * \return output stream
+     */
     friend ostream& operator<<(ostream& ostr, const date& date)
     {
         ostr << int_to_string(date.day_, 2) << "."
@@ -100,6 +118,9 @@ public:
     }
 };
 
+/**
+ * \brief address containing street, no, postal code and city
+ */
 class address final
 {
 private:
@@ -118,6 +139,12 @@ public:
     {
     }
 
+    /**
+     * \brief Input operator of address
+     * \param istr output stream
+     * \param address current address
+     * \return output stream
+     */
     friend istream& operator>>(istream& istr, address& address)
     {
         cout << "Strasse: ";
@@ -131,12 +158,18 @@ public:
         return istr;
     }
 
-    friend ostream& operator<<(ostream& ostr, const address& customer)
+	/**
+	 * \brief Output operator of address
+	 * \param ostr output stream
+	 * \param address current address
+	 * \return output stream
+	 */
+	friend ostream& operator<<(ostream& ostr, const address& address)
     {
-        ostr << "Strasse: " << customer.street_ << endl;
-        ostr << "Hausnummer: " << customer.street_no_ << endl;
-        ostr << "Postleitzahl: " << customer.postal_code_ << endl;
-        ostr << "Ort: " << customer.city_ << endl;
+        ostr << "Strasse: " << address.street_ << endl;
+        ostr << "Hausnummer: " << address.street_no_ << endl;
+        ostr << "Postleitzahl: " << address.postal_code_ << endl;
+        ostr << "Ort: " << address.city_ << endl;
         return ostr;
     }
 };
@@ -421,14 +454,14 @@ int select_motorcycle()
 
 bool validate_reservation(reservation* const reservation)
 {
-    const auto start_sum = reservation->get_start_date().get_sum();
-    const auto end_sum = reservation->get_end_date().get_sum();
+    const auto start_sum = reservation->get_start_date().get_day_num();
+    const auto end_sum = reservation->get_end_date().get_day_num();
     for (auto r : reservations)
     {
         if (r->get_motorcycle() == reservation->get_motorcycle())
         {
-            if (start_sum < r->get_end_date().get_sum() && end_sum > r->get_start_date().get_sum()
-                || end_sum > r->get_start_date().get_sum() && end_sum < r->get_end_date().get_sum())
+            if (start_sum < r->get_end_date().get_day_num() && end_sum > r->get_start_date().get_day_num()
+                || end_sum > r->get_start_date().get_day_num() && end_sum < r->get_end_date().get_day_num())
             {
                 return false;
             }
@@ -463,7 +496,7 @@ void create_reservation()
         system("pause");
         return;
     }
-    if(!current->get_has_driving_license())
+    if (!current->get_has_driving_license())
     {
         cout << "Der Kunde hat keinen entsprechenden Fuehrerschein." << endl;
         system("pause");