var pi=0;
var swapbutton = document.getElementById('swapbutton');
photocount();

function swapphoto(oneimg, direction)
{
var onephoto = document.getElementById(oneimg);
var srcname = onephoto.src.substr(0, onephoto.src.length - 5);

pi += direction;
if (pi < 0)
  {
  pi = photos.length - 1;
  }
pi %= photos.length;

onephoto.src = srcname + photos[pi] + '.jpg';
photocount();

}

function photocount()
{
swapbutton.value = (pi + 1) + ' of ' + photos.length + ' photos';
}