Exercise 5 draft

Added Exercise 5 but incomplete

Informatik_I/Exercise_5/Task_1/calendar.cpp

@@ -0,0 +1,90 @@
+#include "calendar.h"
+#include <string>
+
+// PRE: a year greater or equal than 1900
+// POST: returns whether that year was a leap year
+bool is_leap_year(int year) {
+  if (year >= 1900) {
+    if (year % 4 == 0 && year % 100 != 0)
+      return true;
+    else if (year % 4 == 0 && year % 400 == 0)
+      return true;
+  }
+  return false;
+}
+
+// PRE: a year greater or equal than 1900
+// POST: returns the number of days in that year
+int count_days_in_year(int year) {
+  if (year >= 1900) {
+    if (is_leap_year(year) == true)
+      return 366;
+    return 365;
+  }
+  return 0;
+}
+
+// PRE: a month between 1 and 12 and a year greater or equal than 1900
+// POST: returns the number of days in the month of that year
+int count_days_in_month(int month, int year) {
+  if (year >= 1900 && month > 0 && month <= 12) {
+    if (is_leap_year(year) == false) {
+      if (month % 2 != 0 && month != 2 && month <= 7)
+        return 31;
+      else if (month % 2 == 0 && month != 2 && month > 7)
+        return 31;
+      else if (month == 2)
+        return 28;
+      else
+        return 30;
+    } else {
+      if (month % 2 == 0 && month != 2 && month <= 7)
+        return 31;
+      else if (month % 2 == 0 && month != 2 && month > 7)
+        return 31;
+      else if (month == 2)
+        return 29;
+      else
+        return 30;
+    }
+  }
+  return 0;
+}
+
+// PRE:  n/a
+// POST: returns whether the given values represent a valid date
+bool is_valid_date(int day, int month, int year) {
+  if (day > 0 && day <= count_days_in_month(month, year) && month > 0 &&
+      month <= 12 && year >= 1900)
+    return true;
+  return false;
+}
+
+// PRE: the given values represent a valid date
+// POST: returns the number of days between January 1, 1900 and this date
+// (excluding this date)
+int count_days(int day, int month, int year) {
+  int res_day = 0;
+  if (is_valid_date(day, month, year) == true) {
+    for (int j = 1901; j <= year; ++j) {
+      res_day += count_days_in_year(j);
+    }
+    for (int j = 1; j < month; ++j) {
+      res_day += count_days_in_month(j, year);
+    }
+    res_day += (day - 1);
+  }
+  return res_day;
+}
+
+// PRE: the given values represent a (potentially invalid) date
+// POST: prints the weekday if the date is valid or "invalid date" otherwise.
+//      Everything must be printed in lowercase.
+void print_weekday(int day, int month, int year) {
+  if (is_valid_date(day, month, year) == true) {
+    std::string days[7] = {"sunday",   "monday", "tuesday", "wednesday",
+                           "thursday", "friday", "saturday"};
+    std::cout << days[((count_days(day, month, year) + 1) % 7)];
+  } else
+    std::cout << "invalid date";
+}