Автор: http://www.swissdelphicenter.ch

{
  The factorial of a positive integer is defined as:

  n! = n*(n-1)*(n-2)*(n-3)*...*2*1
  1! = 1
  0! = 1

  Example: 5! = 5*4*3*2*1
 }

// Iterative Solution:

function FacIterative(n: Word): Longint;
var
  f: LongInt;
  i: Integer;
begin
  f := 1;
  for i := 2 to n do
    f := f * i;
  Result := f;
end;

// Recursive Solution:

function FacRecursive(n: Word): LongInt;
begin
  if n > 1 then
    Result := n * FacRecursive(n - 1)
  else
    Result := 1;
end;