Angular Computed Property

HTML

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.6/angular.min.js"></script>
    <script>
        var app = angular.module('app', []);
        app.controller('ctrl', function ($scope) {
            $scope.cols = 0;
            $scope.arr = [];
            $scope.makeArray = function () {
                $scope.arr.length = 0;
                for (var i = 0; i < parseInt($scope.cols) ; i++) {
                    $scope.arr.push(i);
                }
            }
        });
    </script>
    <div ng-app="app">
        <div ng-controller="ctrl">
            <input ng-model="cols" type="text" ng-change="makeArray()" />
            <div ng-repeat="o in arr" style="width: 20px;">hi</div>
        </div>
    </div>