[子程序] 出现Error: Symbol at (1) has no IMPLICIT type

subroutine day1year()
implicit none
integer :: year , mon , days
    common year , mon 
    Integer :: DaysInMonth(12) = [31,28,31,30,31,30,31,31,30,31,30,31]
    if ( ( (MOD(year,4)==0).and.(MOD(year,100)/=0) ) .or. (mod(year,400)==0) ) then
      DaysInMonth(2) = 29
    else
      DaysInMonth(2) = 28
    end if
  days = sum( DaysInMonth )
end subroutine day1year
subroutine dayfromyear( year , mon , day )
implicit none
integer :: day , i , daylast
Integer :: DaysInMonth(12) = [31,28,31,30,31,30,31,31,30,31,30,31]
integer :: k
integer :: years(51) = (/(k,k=1957,2007)/)
integer :: sumday = 0
  do i=1,k,1
  call day1year (years(i))
  sumday = sumday + days
  end do
daylast = sum( DaysInMonth(:mon-1) ) + day +sumday
end subroutine