adding the date class files

lectures/03_classes_I/date_main.cpp

@@ -0,0 +1,29 @@
+// Program:  date_main.cpp
+// Purpose:  Demonstrate use of the Date class.
+
+#include <iostream>
+#include "date.h"
+
+int main() {
+  std::cout << "Please enter today's date.\n"
+	    << "Provide the  month, day and year: ";
+  int month, day, year;
+  std::cin >> month >> day >> year;
+  Date today(month, day, year);
+
+  //Let's show what happens if we try to use today.month (private member variable)
+  Date tomorrow(today.getMonth(), today.getDay(), today.getYear());
+  tomorrow.increment();
+  
+  std::cout << "Tomorrow is ";
+  tomorrow.print();
+  std::cout << std::endl;
+
+  Date Sallys_Birthday(9,29,1995);  
+  if (sameDay(tomorrow, Sallys_Birthday)) {
+    std::cout << "Hey, tomorrow is Sally's birthday!\n";
+  }
+
+  std::cout << "The last day in this month is " << today.lastDayInMonth() << std::endl;
+  return 0;
+}