SHUFFLE.PAS                 COMPLETE LISTING


PROGRAM demonstrate_shuffling;
VAR
  deck           : ARRAY[1..52] OF Integer; {or of anything else}
  saved, i, j    : 1..52;

BEGIN
  {place initial values in array}
  FOR i := 1 TO 52 DO
    deck[i] := i;

  {seed random number generator}
  Randomize;

  {here's the guts of it}

   {shuffle the array - pass *once* through the array, swapping each element
    with another, randomly chosen, element}

  FOR i := 1 TO 52 DO
    BEGIN
      {find another element to swap with. Random returns value between
       0 and 51, so must add 1}
      j := Random(52)+1;
      {make sure not swap element with itself}
      WHILE j = i DO
        j := Random(52)+1;
      {perform the swap}
      saved := deck[i];
      deck[i] := deck[j];
      deck[j] := saved
    END;

  {output for testing purposes}
  FOR i := 1 TO 52 DO
    BEGIN
      Write(deck[i]:3);
      IF i MOD 10 = 0 THEN WriteLn;
    END;
  WriteLn;

END.