/in/foo.cc: In function 'int main()':
/in/foo.cc:21:7: error: no matching function for call to 'Time::Time()'
  Time t1,t2;
       ^~
/in/foo.cc:8:2: note: candidate: Time::Time(int, int, int)
  Time(int x,int y,int z){
  ^~~~
/in/foo.cc:8:2: note:   candidate expects 3 arguments, 0 provided
/in/foo.cc:4:7: note: candidate: constexpr Time::Time(const Time&)
 class Time{
       ^~~~
/in/foo.cc:4:7: note:   candidate expects 1 argument, 0 provided
/in/foo.cc:21:10: error: no matching function for call to 'Time::Time()'
  Time t1,t2;
          ^~
/in/foo.cc:8:2: note: candidate: Time::Time(int, int, int)
  Time(int x,int y,int z){
  ^~~~
/in/foo.cc:8:2: note:   candidate expects 3 arguments, 0 provided
/in/foo.cc:4:7: note: candidate: constexpr Time::Time(const Time&)
 class Time{
       ^~~~
/in/foo.cc:4:7: note:   candidate expects 1 argument, 0 provided
/in/foo.cc:25:13: error: no match for call to '(Time) (int&, int&, int&)'
  t1(x1,y1,z1);
             ^
/in/foo.cc:26:13: error: no match for call to '(Time) (int&, int&, int&)'
  t2(x2,y2,z2);
             ^
/in/foo.cc:28:12: error: invalid use of member function 'int Time::sum()' (did you forget the '()' ?)
  past = t2.sum - t1.sum;
         ~~~^~~
/in/foo.cc:28:21: error: invalid use of member function 'int Time::sum()' (did you forget the '()' ?)
  past = t2.sum - t1.sum;
                  ~~~^~~