Added 1st_day_of_month.cpp

1st_day_of_month.cpp

@@ -0,0 +1,15 @@
+// @COMPILECMD g++ $@ -lboost_date_time
+#include <iostream>
+#include <boost/date_time/gregorian/gregorian.hpp>
+
+int main() {
+    int year = 2023;
+    int month = 7;
+
+    boost::gregorian::date firstDay(year, month, 1);
+    boost::gregorian::date::day_of_week_type weekday = firstDay.day_of_week();
+
+    std::cout << "The first day of " << month << "/" << year << " is a " << weekday << std::endl;
+
+    return 0;
+}