First of all to use functions with $scope you should do something like this:
$scope.checkNow = function() {
...
}
or
$scope.checkNow = checkNow;
function checkNow() {
...
}
About your problem:
You could bind the checkboxes to a property (something like checked), so you can have the items that are checked easily in your controller.
Then, to calculate the total of all checked amount , I' suggest you to use Array.prototype.filter() + Array.prototype.reduce().
Here's a demo based on your original code:
(function() {
angular
.module("app", [])
.controller('MainCtrl', MainCtrl);
MainCtrl.$inject = ['$scope'];
function MainCtrl($scope) {
$scope.checkNow = checkNow;
$scope.checkAmount = {};
$scope.items = [
{
"id": 1
},
{
"id": 2
},
{
"id": 3
}
];
function checkNow() {
$scope.total = $scope.items.filter(function(value) {
return value.checked;
}).reduce(function(a, b) {
return a + b.amount;
}, 0);
}
}
})();
<!DOCTYPE html>
<html ng-app="app">
<head>
<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.5.8/angular.min.js"></script>
</head>
<body ng-controller="MainCtrl">
<div ng-repeat="$item in items">
<label>
Amount: <input type="number" ng-model="$item.amount">
</label>
<label>
Check: <input type=checkbox ng-model="$item.checked">
</label>
</div>
<button type="button" ng-click="checkNow()">Check now</button>
<hr>
<label for="total">Total</label>
<input type="number" id="total" disabled ng-model="total">
</body>
</html>
ngRepeat?