Update quantity not add a new struct - coldfusion

Question

I am currently building a shopping cart, which is using a struct within an array to hold cart information. If the product is already added to the cart and the add to cart button is pressed again I need to update the struct quantity and not add another item to the cart. As the add to cart button is pressed, I first check to see if the array is empty, if not, I loop through the array looking for the product id submitted by the form, if found I simply update the quantity field associated to product id, I then set a variable addNew=no. I have used a cfelse if the product is not found set a variable addNew=yes. I realise what my problem is, if the cart has more than one product, the loop continues and obviously at some point it not find the product id and set the variable addNew=new, which will then as well as update the quantity, will also add the product into a new struct, ending up with product a qty 2 and product a qty 1.
This is the first time using arrays and struct in this way and am just finding my way through, so if my code is not efficient I apologise. Any pointers greatly appreciated;
<cfif arrayLen(session.mycart) GT 0>
<cfloop index="i" from="1" to="#arrayLen(session.mycart)#">
<!---check for existance of the id submitted--->
<cfif session.mycart[i].itemID eq form.itemID>
<!---if the id is matched update the quantity--->
<cfset session.mycart[i].quantity = form.quantity+session.mycart[i].quantity>
<cfset myTotal = form.itemCost*session.mycart[i].quantity>
<cfset session.mycart[i].totalPrice = myTotal>
<!---this will tell the add to cart function not add a new item--->
<cfset addNew = "no">
<cfelse>
<!---as this is a new item tell the add to cart function to add it--->
<cfset addNew ="yes">
</cfif>
</cfloop>
<cfelse>
<!---as the array is empty tel the add to cart function insert the product--->
<cfset addNew ="yes">
</cfif>

Answer 1

There's two things I can think of.
Firstly, you can simplify your code by getting rid of the outer length-check on the array: the loop will cover that for you.
Secondly, when you find and update your quantity (the TRUE part of the IF in the loop), you - at that point - can stop looking for the item. There's no point in continuing through the rest of the array looking for something you've already found. So use CFBREAK at that point to exit the loop.
Another thing to remember, is that one can use CFPARAM to set a variable only if it's not already been set. So if you set addNew to true, and subsequent calls to CFPARAM that variable will leave it as-is. However in this case the CFBREAK approach is better.

Answer 2

You should set the flag to true in the beginning, and then as you loop, if the product is found simply set the flag to false.
<!--- first set the flag to add item to cart --->
<cfset addNew = true>
<cfloop index="i" from="1" to="#arrayLen(session.mycart)#">
<!---check for existance of the id submitted--->
<cfif session.mycart[i].itemID eq form.itemID>
<!---if the id is matched update the quantity--->
<cfset session.mycart[i].quantity = form.quantity+session.mycart[i].quantity>
<cfset myTotal = form.itemCost*session.mycart[i].quantity>
<cfset session.mycart[i].totalPrice = myTotal>
<!---if the item is already in the cart, tell the add to cart function not add a new item--->
<cfset addNew = false>
</cfif>
</cfloop>

Answer 3

Sounds like what you need is a boolean value for each item in the cart, not just one. So you could even add that into the existing structure. Also even though ColdFusion will allow you to use the strings "yes" and "no" as boolean values, I think you'd be better to use true and false instead.
<cfif session.mycart[i].itemID eq form.itemID>
<!---if the id is matched update the quantity--->
<cfset session.mycart[i].quantity = form.quantity+session.mycart[i].quantity>
<cfset myTotal = form.itemCost*session.mycart[i].quantity>
<cfset session.mycart[i].totalPrice = myTotal>
<!---this will tell the add to cart function not add a new item--->
<cfset session.mycart[i].addNew = FALSE>
<cfelse>
<!---as this is a new item tell the add to cart function to add it--->
<cfset session.mycart[i].addNew =TRUE>
</cfif>