<button id="inc">+</button>
<button id="dec">-</button>
<input type="text" name="qty" value="0" />
<script type="text/javascript">
$(function(){
$("#inc").click(function(){
$(":text[name='qty']").val( Number($(":text[name='qty']").val()) + 1 );
});
$("#dec").click(function(){
$(":text[name='qty']").val( Number($(":text[name='qty']").val()) - 1 );
});
});
</script>
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