/tmp/ccrx8pBo.o: In function `Date::number_by_date()':
main.cpp:(.text._ZN4Date14number_by_dateEv[_ZN4Date14number_by_dateEv]+0x114): undefined reference to `Date::leap'
main.cpp:(.text._ZN4Date14number_by_dateEv[_ZN4Date14number_by_dateEv]+0x15e): undefined reference to `Date::leap'
main.cpp:(.text._ZN4Date14number_by_dateEv[_ZN4Date14number_by_dateEv]+0x17a): undefined reference to `Date::not_leap'
main.cpp:(.text._ZN4Date14number_by_dateEv[_ZN4Date14number_by_dateEv]+0x1c4): undefined reference to `Date::not_leap'
/tmp/ccrx8pBo.o: In function `Date::date_by_number(int)':
main.cpp:(.text._ZN4Date14date_by_numberEi[_ZN4Date14date_by_numberEi]+0x1a0): undefined reference to `Date::leap'
main.cpp:(.text._ZN4Date14date_by_numberEi[_ZN4Date14date_by_numberEi]+0x1ea): undefined reference to `Date::leap'
main.cpp:(.text._ZN4Date14date_by_numberEi[_ZN4Date14date_by_numberEi]+0x20a): undefined reference to `Date::leap'
main.cpp:(.text._ZN4Date14date_by_numberEi[_ZN4Date14date_by_numberEi]+0x22d): undefined reference to `Date::not_leap'
main.cpp:(.text._ZN4Date14date_by_numberEi[_ZN4Date14date_by_numberEi]+0x277): undefined reference to `Date::not_leap'
main.cpp:(.text._ZN4Date14date_by_numberEi[_ZN4Date14date_by_numberEi]+0x293): undefined reference to `Date::not_leap'
collect2: error: ld returned 1 exit status