Question: I'm wanting to add a class 'slide-number-x' to an element within each slide in a slider, with the 'x' representing the slide number in the dom. 

So, for example this simple HTML markup:

```
<div class="slider">
    <div class="slide"><div class="slide-title"></div></div>
    <div class="slide"><div class="slide-title"></div></div>
    <div class="slide"><div class="slide-title"></div></div>
    <div class="slide"><div class="slide-title"></div></div>
</div>

```

Would become:

```
<div class="slider">
    <div class="slide slide-number-1"><div class="slide-title"></div></div>
    <div class="slide slide-number-2"><div class="slide-title"></div></div>
    <div class="slide slide-number-3"><div class="slide-title"></div></div>
    <div class="slide slide-number-4"><div class="slide-title"></div></div>
</div>

```

I thought this would work:

```
$('.slide').each(function(i){
  $(this).addClass('slide-number'i+1);
});

```

Any help or ideas?

Many thanks,
R

Answer: 
You forgot the concatenation operator (`+`), use:

```
$('.slide').each(function(i){
  $(this).addClass('slide-number-' + (i+1));
});

```
You are missing the concatenation operator. Also, the convention for incrementing a value in JavaScript is the the double plus.

```
$('.slide').each(function(i){
  $(this).addClass('slide-number-' + ++i);
});

```