writefile Subroutine

  subroutine writefile(this,C81filename)
  !! Writes C81 class data to C81 file
  class(C81_class) :: this
    character(len=*), intent(in) :: C81filename
    integer :: i, j
    logical :: fileExists
    character(len=10) :: formatChar
    character(len=1) :: overwriteOption

    inquire(file=C81filename, exist=fileExists)
    if (fileExists) then
      print*, 'File '//trim(C81filename)//' already exists!'
      write(*,'(A)',advance='no') ' Okay to overwrite (y/n)? '
      read(*,*) overwriteOption
      print*
      if ((overwriteOption .ne. 'y') .and. (overwriteOption .ne. 'Y')) stop
    endif

    open(unit=10,file=C81filename, action='write')

    this%ML = size(this%MaL,1)
    this%MD = size(this%MaD,1)
    this%MM = size(this%MaM,1)
    this%NL = size(this%AL,1)
    this%ND = size(this%AD,1)
    this%NM = size(this%AM,1)

    write(10,100) this%airfoilName,this%ML,this%NL,this%MD,this%ND,this%MM,this%NM
    ! Lift
    write(10,101) (this%MaL(i),i=1,min(9,this%ML))
    if (this%ML>9) then 
      write(formatChar,'(A4,I1,A5)') '(7X,',this%ML-9,'F7.3)'
      write(10,formatChar) (this%MaL(i),i=10,this%ML)
    endif
    do i=1,this%NL
      write(10,102) this%AL(i), (this%CL(i,j),j=1,min(9,this%ML))
      if (this%ML>9)  write(10,formatChar) (this%CL(i,j),j=10,this%ML)
    enddo

    ! Drag
    write(10,101) (this%MaD(i),i=1,min(9,this%MD))
    if (this%MD>9) then 
      write(formatChar,'(A4,I1,A5)') '(7X,',this%MD-9,'F7.3)'
      write(10,formatChar) (this%MaD(i),i=10,this%MD)
    endif
    do i=1,this%ND
      write(10,102) this%AD(i), (this%CD(i,j),j=1,min(9,this%MD))
      if (this%MD>9)  write(10,formatChar) (this%CD(i,j),j=10,this%MD)
    enddo

    ! Moment
    write(10,101) (this%MaM(i),i=1,min(9,this%MM))
    if (this%MM>9) then 
      write(formatChar,'(A4,I1,A5)') '(7X,',this%MM-9,'F7.3)'
      write(10,formatChar) (this%MaM(i),i=10,this%MM)
    endif
    do i=1,this%NM
      write(10,102) this%AM(i), (this%CM(i,j),j=1,min(9,this%MM))
      if (this%MM>9)  write(10,formatChar) (this%CM(i,j),j=10,this%MM)
    enddo

    close(10)

    100 format (A30,6I0.2)
    101 format (7X,9F7.3)
    102 format (F7.2,9F7.3)
  end subroutine writefile