rem - return the digital sum of n represented as a string
function digitalsum(nstr = string) = integer
   var i, slen, sum = integer
   var ch = char
   slen = len(nstr)
   sum = 0
   for i = 1 to slen
     ch = mid(nstr, i, 1)
     rem - don't process leading or embedded spaces, etc.
     if ch >= '0' and ch <= '9' then
        sum = sum + (ch - '0')
   next i
end = sum

var nstr = string
var droot, pers = integer

0again
   rem - input1 does not advance to next line; control-C will exit
   input1 "What number"; nstr
   droot = digitalsum(nstr)
   pers = 1
   while droot > 9 do
      begin
         droot = digitalsum(str$(droot))
         pers = pers + 1
      end
   print " digital root ="; droot; " persistence ="; pers
   goto 0again

end