diff --git a/src/Motorradvermietung.cpp b/src/Motorradvermietung.cpp
index 1893e3d..39382a4 100644
--- a/src/Motorradvermietung.cpp
+++ b/src/Motorradvermietung.cpp
@@ -25,6 +25,11 @@ T ask_question(const string& question)
     return value;
 }
 
+/**
+ * \brief Returns true if answer was 'J'. False if user answered with 'N'
+ * \param question The question for user input.
+ * \return 
+ */
 bool ask_question(const string& question)
 {
     while (true)
@@ -42,10 +47,16 @@ bool ask_question(const string& question)
     }
 }
 
-auto int_to_string(const unsigned int value, const unsigned int numbers = 0) -> string
+/**
+ * \brief Converts a int to string and fill up with '0' at first position.
+ * \param value the integer value.
+ * \param digits Number of digits to fill
+ * \return Formatted integer as string
+ */
+auto int_to_string(const unsigned int value, const unsigned int digits = 0) -> string
 {
     auto str = to_string(value);
-    const auto len = numbers > str.length() ? numbers - str.length() : 0;
+    const auto len = digits > str.length() ? digits - str.length() : 0;
     for (unsigned int i = 0; i < len; ++i)
     {
         str.insert(0, "0");