<!DOCTYPE html>
<html data-ng-app="MyApp">

<head>
  <script data-require="angularjs@1.5.5" data-semver="1.5.5" src="https://code.angularjs.org/1.5.5/angular.js"></script>
  <link rel="stylesheet" href="style.css" />
  <script src="script.js"></script>
</head>

<body data-ng-controller="InvoiceController as invoice">
  <input id="inputCurr" type="number" min="0" ng-model="invoice.inputValue">
  <select data-ng-model="invoice.inCurr">
    <option data-ng-repeat="curr in invoice.currencies">{{curr}}</option>
  </select>
  <br/>
  <br/>
  <input id="oututCurr" type="number" min="0" ng-model="invoice.output()">
  <select data-ng-model="invoice.outCurr">
    <option data-ng-repeat="curr in invoice.currencies">{{curr}}</option>
  </select>
</body>

</html>
var app = angular.module("MyApp", []).
controller("InvoiceController", function() {
  this.currencies = ['INR', 'EUR', 'USD'];
  this.inCurr = "INR";
  this.outCurr = "EUR";
  this.inrToForeignRates = {
    INR: 1,
    EUR: 0.013,
    USD: 0.015
  };
  this.inputValue = 10;
  this.outputValue = function(input, inCurr, outCurr) {
    return input * this.inrToForeignRates[outCurr] / this.inrToForeignRates[inCurr];
  };
  this.output = function() {
    return this.outputValue(this.inputValue, this.inCurr, this.outCurr);
  };
});