// initialise current image number to 0
var currImg = 0;

// create array to hold images for slideshow  
var pics = new Array();
    pics[0] = new Image();
    pics[1] = new Image();
    pics[2] = new Image();
    pics[3] = new Image();

// function to preload images
// this should be called by the onload event of the body tag
function preloadImages() {

  // initalise array with data
  pics[0].src = "images/pub1.jpg";
  pics[1].src = "images/pub2.jpg";
  pics[2].src = "images/pub3.jpg";
  pics[3].src = "images/pub4.jpg";

  // add slideshow controls
  var parent = document.getElementById("sshowCont");
  // create link
  var newLink = document.createElement('a');
  newLink.href = "javascript:changeImage('')";
  // create link text
  var linkText = document.createTextNode("Next");
  newLink.appendChild(linkText);
  var newPara = document.createElement('p');
  newPara.appendChild(newLink);
  parent.appendChild(newPara);
}

// function to change image
function changeImage(imageName) {

  var imageNo;
  if (currImg == 3) {
     currImg = 0;
     imageNo = currImg;
  } else {
     currImg ++;
     imageNo = currImg;
  }
  document[imageName].src = pics[imageNo].src;
}