Please help me out on this question " Input Data Using Forms " trailhead task: I used <Lightning:> tags as per trailhead suggested

<aura:component >
    <aura:attribute name="newItem" type="Camping_Item__c"
                    default="{ 'sobjectType': 'Camping_Item__c',
                             'Name': '',
                             'Quantity__c': 0,
                             'Price__c': 0,
                             'Packed__c': false }"/>
    <aura:attribute name="items" type="Camping_Item__c[]"/>
    <!-- CREATE NEW ITEM FORM -->
    <form class="slds-form--stacked">
                        <lightning:input aura:id="itemname" label="Camping Item Name"
                                         name="itemname"
                                         value="{!v.newItem.Name}"
                                         required="true"/> 
                        <lightning:input type="number" aura:id="quantity" label="Quantity"
                                         name="itemquantity"
                                         value="{!v.newItem.silk__Quantity__c}"
                                         /> <!--placeholder="1"  min="1"-->
                        <lightning:input aura:id="price" label="Price"
                                         formatter="currency"
                                         name="itemprice"
                                         value="{!v.newItem.silk__Price__c}"/>
                        <lightning:input type="checkbox" aura:id="packed" label="Packed?"  
                                         name="itempacked"
                                         checked="{!v.newItem.silk__Packed__c}"/>
                        <lightning:button label="Create Camping Item" 
                                          class="slds-m-top--medium"
                                          variant="brand"
                                          onclick="{!c.clickCreateItem}"/>
    </form>
    <!-- / CREATE NEW ITEM FORM -->
    <c:campingHeader/>
    <div class="slds-card slds-p-top--medium">
        <section class="slds-card__body">
            <div id="list" class="row">
                <aura:iteration items="{!v.items}" var="item">
                    <c:campingListItem item="{!item}"/>
                </aura:iteration>
            </div>
        </section>
    </div>
</aura:component>

CampingListController.js

({
    clickCreateItem: function(component, event, helper) {
        // Simplistic error checking
        var validItem = true;
        // Name must not be blank
        var nameField = component.find("itemname");
        var itemname = nameField.get("v.value");
        if ($A.util.isEmpty(itemname)){
            validItem = false;
            nameField.set("v.errors", [{message:"Item name can't be blank123."}]);
        }
        else {
            nameField.set("v.errors", null);
        }
        // Quantity must not be blank
        var quantityField = component.find("quantity");
        var quantity1 = nameField.get("v.value");
        //alert('Alert quantity'+quantity);
        console.log(quantity1);
        if ($A.util.isEmpty(quantity1)){
            validItem = false;
            quantityField.set("v.errors", [{message:"Quantity can't be blank."}]);
        }
        else {
            quantityField.set("v.errors", null);
        }
        var priceField = component.find("price");
        var price = priceField.get("v.value");
        if ($A.util.isEmpty(price)){
            validItem = false;
            priceField.set("v.errors", [{message:"Price can't be blank."}]);
        }
        else {
            quantityField.set("v.errors", null);
        }  
        if(validItem){
            var newItem = component.get("v.newItem");
            var item = JSON.parse(JSON.stringify(newItem)); 
            console.log(item);
            var itemarray = component.get("v.items");
            itemarray.push(item);
            component.set("v.items",itemarray); 
        }
        component.set("v.newItem",{ 'sobjectType': 'Camping_Item__c','Name': '','Quantity__c': 0,
                                       'Price__c': 0,'Packed__c': false});
    }
})

CampinListItems.cmp

<aura:component >
    <aura:attribute name="Item" type="Camping_Item__c" required="true"/>
    <p>Name: {!v.Item.Name}</p>
    <p>	<lightning:formattedNumber value="{!v.Item.Price__c}" style="currency"/></p>
    <p><lightning:formattedNumber value="{!v.Item.Quantity__c}" /></p>
    <p><lightning:input type="toggle" label="Packed?" name="Packed" checked="{!v.Item.Packed__c}"/></p>
    <p><lightning:button label="Packed!" onclick="{!c.packItem}"/></p>
</aura:component>

CampingHeader.cmp

<aura:component >
    <lightning:layout class="slds-page-header slds-page-header--object-home">
        <lightning:layoutItem >
            <lightning:icon iconName="action:goal" alternativeText="My Component Item"/>
        </lightning:layoutItem>
        <lightning:layoutItem padding="horizontal-small">
            <div class="page-section page-header">
                <h1 class="slds-text-heading--label">Component Item</h1>
                <h2 class="slds-text-heading--medium">My Component Item</h2>
            </div>
        </lightning:layoutItem>
    </lightning:layout>
    <!-- / PAGE HEADER -->
</aura:component>