Edit in JSFiddle

angular.module('shopping',[])
			.value('shopping_cart_operations',{
				items : [
					{Name: "Soap", Price: "25", Quantity: "10"},
					{Name: "Shaving cream", Price: "50", Quantity: "15"},
					{Name: "Shampoo", Price: "100", Quantity: "5"}
					],
				addItem: function(item){
					this.items.push(item);
				},
				totalPrice: function(){
					var total = 0;
					for(count=0;count<this.items.length;count++){
						total += this.items[count].Price*this.items[count].Quantity;
					}
					return total;
				},
				removeItem: function(index){
					this.items.splice(index,1);
				}
				
			})
			.filter('rupee',function(){
				return function(item){
					return "Rs. "+item;
				}
			})
			.directive('validPrice',function(){
				return{
					require: "ngModel",
					link: function(scope, elm, attrs, ctrl){
						
						var regex=/^\d{2,4}(\.\d{1,2})?$/;
						ctrl.$parsers.unshift(function(viewValue){
							var floatValue = parseFloat(viewValue);
							if( floatValue >= 50 && floatValue <=5000 && regex.test(viewValue)){
								ctrl.$setValidity('validPrice',true);
								//return viewValue;
							}
                            else{
							    ctrl.$setValidity('validPrice',false);
                            }
							return viewValue;
						});
					}
				};
			});
  
	function ShoppingCartCtrl($scope,shopping_cart_operations)  {
		$scope.items = shopping_cart_operations.items;
		$scope.item = {};

		$scope.addItem = function(item) {
			shopping_cart_operations.addItem(item);
			$scope.item = {}; 
			$scope.itemForm.$setPristine();
		};
    
		$scope.totalPrice = shopping_cart_operations.totalPrice;
		
		$scope.removeItem = function(index){
			shopping_cart_operations.removeItem(index);
		};
		
		$scope.mySortFunction = function(item) {
			if(isNaN(item[$scope.sortExpression]))
				return item[$scope.sortExpression];
			return parseInt(item[$scope.sortExpression]);
		};
		
		$scope.name=/^[a-zA-Z ]*$/;
		
        $scope.integerval=/^\d*$/;
	}

<div ng-app="shopping">
		<div ng-controller="ShoppingCartCtrl">
		<div>Sort by: 
            <select ng-model="sortExpression">
					<option value="Name">Name</option>
					<option value="Price">Price</option>
					<option value="Quantity">Quantity</option>
				</select>
            </div>
			<br />
			<div><strong>Filter Results</strong></div>
			<table>
				<tr>
					<td>By Any: </td>
					<td><input type="text" ng-model="search.$" /></td>
				</tr>
				<tr>
					<td>By Name: </td>
					<td><input type="text" ng-model="search.Name" /></td>
				</tr>
				<tr>
					<td>By Price: </td>
					<td><input type="text" ng-model="search.Price" /></td>
				</tr>
				<tr>
					<td>By Quantity: </td>
					<td><input type="text" ng-model="search.Quantity" /></td>
				</tr>
			</table>
            <br />
			<table border="1">
				<thead>
					<tr>
						<td>Name</td>
						<td>Price</td>
						<td>Quantity</td>
						<td>Remove</td>
					</tr>
				</thead>
				<tbody>
					<tr ng-repeat="item in items | orderBy:mySortFunction | filter:search">
						<td>{{item.Name}}</td>
						<td>{{item.Price | rupee}}</td>
						<td>{{item.Quantity}}</td>
						<td><input type="button" value="Remove" ng-click="removeItem($index)" /></td>
					</tr>
				</tbody>
			</table>
			<br />
			<div>Total Price: {{totalPrice()}}</div>
			<br />
			<form novalidate name="itemForm">
				<table>
					<tr>
						<td>Name: </td>
						<td><input name="name" type="text" ng-model="item.Name" required ng-pattern="name" /></td>
					</tr>
					<tr>
						<td>Price: </td>
						<td><input name="price" type="text" ng-model="item.Price" required  valid-price /></td>
					</tr>
					<tr>
						<td>Quantity: </td>
                        <td><input name="quantity" type="number" ng-model="item.Quantity" min="1" max="90" ng-pattern="integerval" required /></td>
					</tr>
					<tr>
						<td colspan="2"><input type="Button" value="Add" ng-click="addItem(item)" ng-disabled="itemForm.$invalid" /> </td>
					</tr>
				</table>
			</form>
            <div ng-show="itemForm.name.$dirty && itemForm.name.$invalid">
                <span ng-show="itemForm.name.$error.required">Name cannot be left blank</span>
                <span ng-show="itemForm.name.$error.pattern">Name cannot contain numbers or special characters</span>
            </div>
            <div ng-show="itemForm.price.$dirty && itemForm.price.$invalid">
                <span ng-show="itemForm.price.$error.required">Price cannot be blank</span>
                <span ng-show="itemForm.price.$error.validPrice">Price should be a number between 50 and 5000 with maximum 2 digits after decimal point</span>
            </div>
            <div ng-show="itemForm.quantity.$dirty && itemForm.quantity.$invalid">
                <span ng-show="itemForm.quantity.$error.required">Quantity cannot be blank</span>
                <span ng-show="itemForm.quantity.$error.pattern || itemForm.quantity.$error.min || itemForm.quantity.$error.max">Quantity should be an integer between 1 and 90</span>
            </div>
		</div>
	</div>

.bold { font-weight:bold; }

table td{
    padding: 10px;
}

table th{
    font-weight: bold;
    text-align: center;
}

input.ng-invalid.ng-dirty {
		background-color: #FA787E;
	}
	
	input.ng-valid.ng-dirty {
		background-color: #78FA89;
	}

span[ng-show]{
    color: #FA787E;
}