Hello, I've got another assignment for javascript class that I'm struggling with. Here's the code:

PHP Code:
//the check mark boxes
<div id="myboxes">
<
p>What do you love?</p>
<
p><input name="chocoCake" type="checkbox" value="chocolate cake" /><label for="chocoCake">Chocolate Cake</label></p>

<
p><input name="baseball" type="checkbox" value="baseball" /><label for="baseball">Baseball</label></p>

<
p><input name="shinyThings" type="checkbox" value="Shiny Things" /><label for="shinyThings">Shiny Things</label></p>

<
p><input name="puppies" type="checkbox" value="puppies" /><label for="puppies">Puppies</label></p>

<
p><input name="vacation" type="checkbox" value="Vacation" /><label for="vacation"Vacation</label></p>

<
p><input type="button" value="Check All" onclick="checkAll()" /></p>

<
p><input type="button" value="Uncheck All" onclick="unCheckAll()" /></p>
</
div>

//the javascript
function checkAll() {
     var 
checkboxes = new Array();
     
checkboxes document.getElementsByTagName('input');

     for (var 
0checkboxes.lengthi++) {
         if (
checkboxes[i].type == 'checkbox') {
             
checkboxes[i].setAttribute('checked'true)
         }
     }
 }
 
 function 
unCheckAll() {
     var 
uncheckboxes = new Array();
     
uncheckboxes document.getElementsByTagName('input');

     for (var 
0uncheckboxes.lengthi++) {
         if (
uncheckboxes[i].type == 'checkbox') {
             
uncheckboxes[i].setAttribute('unchecked'false)
         }
     }
 } 
As it stands, the first "Check All" box works great. But, when I use the "Uncheck All" button, nothing happens. What am I missing?