{Clear the screen, and put up a title}
display_title(*** Orbital Positions ***)

{Set the default argument for first run through}
if (s1=.)
   set_string(s1,Sun)
end_if

{For which object shall we make the calculation?}
ask_for_string(Calculate the position of which body,s1)

{Use the character variable c1 to flag an error}
set_character(c1,N)

{Check for allowed calculation types}
if (s1=sun)
    set_character(c1,Y)
end_if
if (s1=moon)
    set_character(c1,Y)
end_if
if (s1=mercury)
    set_character(c1,Y)
end_if
if (s1=venus)
    set_character(c1,Y)
end_if
if (s1=mars)
    set_character(c1,Y)
end_if
if (s1=jupiter)
    set_character(c1,Y)
end_if
if (s1=saturn)
    set_character(c1,Y)
end_if
if (s1=uranus)
    set_character(c1,Y)
end_if
if (s1=neptune)
    set_character(c1,Y)
end_if
if (s1=elliptical)
    set_character(c1,Y)
end_if
if (s1=parabolic)
    set_character(c1,Y)
end_if

{Calculate the position and display the result if allowed}
if (c1=Y)
   find_position(s1)
   display_position(s1)
end_if

{Raise an objection if the requested calculation is illegal}
if (c1!Y)
   set_normal_text(12)
   new_line
   write_string(   +++ )
   write_string(s1)
   write_string( is not an allowed calculation type)
   new_line
   new_line
   set_normal_text(7)
end_if

{Another calculation?}
ask_for_repeat