How to find the second Tuesday in October of a given year in C++?

[helloworld2020]

For example, given 2019, October, return 12 since the second Tuesday on October 2019 is 12th. I know how to do it in java. I want to implement it in C++, but I do not know what libraries I should use.

The following is the Java code:
public int date(int year) {
LocalDate start = LocalDate.of(year, 10, 1);

if (start.getDayOfWeek() == DayOfWeek.TUESDAY)
return start.plusWeeks(1).getDayOfMonth();

return start.with(TemporalAdjusters.next(DayOfWeek.TUESDAY)).plusWeeks(1).getDayOfMonth();
}

[salem c]

https://en.cppreference.com/w/c/chrono/mktime

[lastchance]

Find what week day the first of the month was and work from that.

#include <iostream>
#include <ctime>
using namespace std;

const char * weekday[] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };

int getFirstWeekDayOfMonth( int year, int month )
{
   tm TM = { 0, 0, 0, 1, month - 1, year - 1900 };
   mktime( &TM );
   return TM.tm_wday;
}
    
    
int main ()
{
   int year, month;
   cout << "Enter year: ";   cin >> year;
   cout << "Enter month (1-12): ";  cin >> month;
  
   int first = getFirstWeekDayOfMonth( year, month );
   cout << "The first day of the month was a " << weekday[first] << '\n';
}

March this year:

Enter year: 2019
Enter month (1-12): 3
The first day of the month was a Friday

[Cubbi]

Second tuesday in October 2019 is the 8th (first tuesday is the 1st)

It's really neat in C++20:

#include <chrono>
#include <iostream>
using namespace std::chrono;
int main() {
  auto d = year_month_day{ Tuesday[2] / October / 2019y } ; // 2019-10-08
  std::cout << d.day() << '\n'; // 8
}

(until C++20 comes to compiler near you, you can use date.h: live demo https://wandbox.org/permlink/IJfTLWVZz2ASdOjo


Edit: to make it match that Java method signature in the original post,

int date(int y) {
  return (unsigned)year_month_day{ Tuesday[2] / October / year{y} }.day();
}

live demo https://wandbox.org/permlink/7CnWQ5FaeKV2OCKn

[lastchance]

#include <iostream>
#include <ctime>
using namespace std;

const char * weekday[] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };

int getFirstWeekDayOfMonth( int year, int month )
{
   tm TM = { 0, 0, 0, 1, month - 1, year - 1900 };
   mktime( &TM );
   return TM.tm_wday;
}  

int getUmpteenthDayOfMonth( int year, int month, int day, int n )
{
   int day1 = 1 + day - getFirstWeekDayOfMonth( year, month );
   if ( day1 < 1 ) day1 += 7;
   return day1 + ( n - 1 ) * 7;
}

int main ()
{
   int n = 2;       // The particular day count
   int day = 2;     // Tuesday
   int month = 10;  // October
   int year;   cout << "Enter year: ";   cin >> year;
   
   cout << "Required day = " << getUmpteenthDayOfMonth( year, month, day, n ) << '\n';
}

Enter year: 2019
Required day = 8