/in/foo.cc: In function 'int main()':
/in/foo.cc:23:8: warning: statement has no effect [-Wunused-value]
  month2-month1;
  ~~~~~~^~~~~~~
/in/foo.cc:9:30: warning: unused variable 'month' [-Wunused-variable]
  int month1,month2,day1,day2,month,day3,day4;
                              ^~~~~
/in/foo.cc:9:36: warning: variable 'day3' set but not used [-Wunused-but-set-variable]
  int month1,month2,day1,day2,month,day3,day4;
                                    ^~~~
/in/foo.cc:9:41: warning: variable 'day4' set but not used [-Wunused-but-set-variable]
  int month1,month2,day1,day2,month,day3,day4;
                                         ^~~~