window.onload = function(){
    var nextButton = document.getElementById("next");
    nextButton.onclick = next;

    var previousButton = document.getElementById("previous");
    previousButton.onclick = previous;

    var numPics = 13;
    
    var current = 1;

    var path = "images/scroll";

    var scroller = document.getElementById("scroller");
     

    function next(){
        current = current + 1;
        if(current > numPics){
            current = 1;
        }
        scroller.src = path + current +".jpg";
    }

    function previous(){
        current = current - 1;
        if(current < 1){
            current = numPics;
        }
        scroller.src = path + current +".jpg";
    }
}