Could someone please tell me what I am doing wrong? I'm not a newbie at programming but I feel like it tonight! Every time I increment the incrementing variable it throws a fit! When add one to it, it behaves fine, but if I try to add one more to it it wants to add 2 more. And then if I try to de-increment it wants to subtract from the original number that it was assigned to. 
I've tried: 
i++;
i = i+1;
i = i++;
Nothing seems to work. It's got to be a stupid mistake.
Press the buttons to increment and de-increment. 
http://michaelreynolds.net/iphone/
here's the code:
var dayNum = 30;
//----------------------------------------------------------------------
$.jQTouch({
        icon: 'dailyqoteicon.png',
        statusBar: false,
        initializeTouch: 'a.touch'
    });
//----------------------------------------------------------------------
$(document).ready(function(){
    //$(function(){});
    $(function(){
        $('a.touch').swipe( function(event, info){
            //alert("jQTouch swipe event"); 
            //alert(info.direction);
        });
    });
    $(function updateVerse(){
        //alert("updateVerse called");
        $.ajax({
            type: "GET",
            dataType: 'JSON',
            data: 'day='+ dayNum,
            url: 'forward.php',
            success: function(data){
                var obj = $.parseJSON(data);
                $("h2.quote").html("");
                $("h3.reference").html("");
                $("h2.quote").append(obj.quote);
                $("h3.reference").append(obj.reference, " ",  obj.version);
                //$("span.version").append(obj.version);
                //-----------------------------------
                // JSON string {"id":"1","quote":"For to me, to live is Christ, and to die is gain","reference":"Philippians 1:21","version":"NKJV"}
            },
            error: function(request, error){
                alert("problem retrieving json data string");
            }
        });
        function addDayNum(){
            dayNum = dayNum + 1;
            //dayNum = dayNum++;
        }
        function subDayNum(){
            dayNum = dayNum - 1;
            //dayNum = dayNum--;
        }
        $("div#header a.next").tap( function(){
            addDayNum();
            //dayNum++;// doesn't work at all
            //dayNum = dayNum + 1;//doesn't work at all
            updateVerse();
            //alert(dayNum);
            //alert("next clicked");
        });
        $("div#header a.prev").live('click', function(){
            subDayNum();
            //dayNum--;//doesn't work at all
            //dayNum = dayNum - 1;// doesn't work at all
            updateVerse();
            //alert(dayNum);
            //alert("previous clicked");
        });
    });
});