Clear the previous input once the selection is selected - angularjs

Question

How would I clear the input box once the user select from dropdown using angularjs.
every time clear the input box once the selection is made.
here is what I put together the sample:
http://jsfiddle.net/abuhamzah/jb1j3w7x/
<div ng-app="myApp" ng-controller="MyCtrl">
<div class="col-xs-12">
<label class="col-xs-6 control-label">Type:</label>
<div class="col-xs-6">
<select name="type" ng-model="payment.type" ng-dropdown required ng-change="changeme(payment.type)" >
<option ng-option value="Cash">Cash</option>
<option ng-option value="Check">Check</option>
<option ng-option value="Money Order">Money Order</option>
</select>
</div>
</div>
{{ payment.cash }}
<div class="col-xs-12" id="cash" ng-if="payment.type == 'Cash'">
<div >
<label class="col-xs-6 control-label">Cash :</label>
<div class="col-xs-6">
</div>
</div>
</div>
<div class="col-xs-12" id="check" ng-if="payment.type == 'Check'">
<div >
<label class="col-xs-6 control-label">check :</label>
<div class="col-xs-6">
</div>
</div>
</div>
<div class="col-xs-12" id="money_order" ng-if="payment.type == 'Money Order'">
<div >
<label class="col-xs-6 control-label">money_order :</label>
<div class="col-xs-6">
</div>
</div>
</div>
<div class="col-xs-12" ng-if="payment.type == 'Check' || payment.type == 'Money Order' || payment.type == 'Cash'">
<div >
<div class="col-xs-6"><input type="number" class="form-control" ng-model="payment_input"/>{{payment.type}}</div>
</div>
</div>
var myApp = angular.module('myApp',[]);
function MyCtrl($scope) {
$scope.changeme = function() {
alert(payment.type);
payment_input='';
}
}

Answer 1

You can do this more easily with $watch, which is designed for this purpose.
In your controller:
$scope.$watch('payment.type', function (newVal, oldVal) {
$scope.payment_input = 0;
// anything else you want to do when the payment type is changed
})
Now whenever payment.type is changed, these lines will be executed.
Here are more docs: https://docs.angularjs.org/api/ng/type/$rootScope.Scope
EDIT
Here is a working fiddle with your code: http://jsfiddle.net/jb1j3w7x/5/

Answer 2

You need to use ng-show instead of ng-if for input element container because the following reason
The ngIf directive removes or recreates a portion of the DOM tree
based on an {expression}. If the expression assigned to ngIf evaluates
to a false value then the element is removed from the DOM, otherwise a
clone of the element is reinserted into the DOM.
Approach 1: (using controller)
Working demo: http://jsfiddle.net/jb1j3w7x/2/
Approach 2: (you can update the model without controller)
Working demo: http://jsfiddle.net/jb1j3w7x/4/
Also,
You have missed to add $scope for updating the number field
Number field should be updated as number. we cant update as empty
text