🚀 go-pugleaf

thecrow@iconn.net (The Crow) wrote:

>Here is what I am trying to do, I want to find the last NON-ZERO digit of a 
>given factorial.  For instance,

>5! = 120

>so the last non-zero digit is 2.  I want to be able to do this up to 1000.  
>Problem is, no matter how huge of a data-type you use, there isn't any way for 
>the computer to handle 1000!, it is however possible to find the last non-zero 
>digit somehow.  One thing I have tried is as I went through mulitplying the 
>series of numbers in the factorial (5 * 4 * 3 * 2) I would remove all the 
>trailing ZEROS, I got this to work up to 789, but it wont work with 1000 and i 
>am not really sure why.  If anyone has a clue how I can do this let me know.

>-- 
>The Crow - thecrow@iconn.net
>"It can't rain all the time"
>-Kryptology

program TryThis(input,output);

   function RMNZD(
      n                        : integer
       )                       : integer;
   { determine the right most non-zero digit } begin
      while n mod 10 = 0 do
         n:=n div 10;
      RMNZD:=N mod 10;
       end { RMNZD };

var
   digit : byte;
   i     : integer;
   n     : integer;
{ } begin
   readln(input,n);
   if n > 1 then { only treat n > 1 } begin
      digit:=1;
      for i:=2 to n do
         digit:=RMNZD(digit)*RMNZD(i);
      writeln(output,RMNZD(digit));
       end;
    end { TryThis }.