Setting dynamic css-background image in wordpress post [jQuery]

[Kay]

I have a site based on wordpress and I want to change the header image for every single post. As every post has its own 'id', I want to make a jquery function which would read the post 'id' (for example id="post-8") and would set a background image named the same way, so I just have to make a new image and upload it everytime I write a new post, and no css changes would be needed.I have very bare idea of jquery, but my bro's help I got the following code:\[code\]var txt1 = "post-"; for (var i=0; i<1000; i++){ var elementId = txt1.concat(i); var postimg1 = "url(../images/"; var postimg2 = ".jpg)"; var postimgfull = postimg1 + elementId + postimg2; var element = $("#" + elementId); if (element != null) { $(".posthead").css('background-image', postimgfull); }else { break; }\[/code\]But using that I don't get the image named "post-8.jpg", what I get is an image named "post-999.jpg".Can you help me here?Thankyou mates!