function myMain() {
  var deck =[];
  var nc = Number(prompt("num cards?"));
  
  // load the initial deck in order
  for (var i=0; i<nc; i++) { deck[i] = i; }
  //alert(deck);
  alert(deck[0]); alert(deck[6]); alert(deck[12]);
  
  // shuffle the deck
  deck = shuffle(deck);
  
  //alert(deck);
  alert(deck[0]); alert(deck[6]); alert(deck[12]);
  
  return; 
}

function shuffle (deck) {
  var n1, n2, tmp;
  var nSwaps = 10;
  
  for (t=0; t<nSwaps; t++) {
    n1 = Math.floor(Math.random()*deck.length);
    n2 = Math.floor(Math.random()*deck.length);
    tmp = deck[n1];
    deck[n1] = deck[n2];
    deck[n2] = tmp;
  }
  
  return deck;
}


myMain();