foo.cc: In member function 'int Time::de(Time&)':
foo.cc:37:13: warning: unused variable 'num' [-Wunused-variable]
   37 |         int num = 0;
      |             ^~~
foo.cc: In member function 'int Date::de(Date&)':
foo.cc:94:18: warning: statement has no effect [-Wunused-value]
   94 |             for (m; m < obj.m; m++)
      |                  ^
foo.cc:96:18: warning: statement has no effect [-Wunused-value]
   96 |             for (y; y <= obj.y; y++)
      |                  ^
foo.cc:105:18: warning: statement has no effect [-Wunused-value]
  105 |             for (y; y < obj.y-1; y++)
      |                  ^