数据结构与算法之Stack（栈）的应用——用stack实现一个计算器-/bin/calc.dart

计算器的bin/calc.dart 可执行代码：

 import 'dart:io';

 import 'package:data_struct/stack/sample/calculator.dart';

 void main() {

   print('please input the expression:');

   var ins = stdin.readLineSync();

   while (ins != 'exit') {

     try {

       var r = calc(ins);

       print('\n the result is: $r');

     } on FormatException {

       print('Format error!');

     } on Exception catch (e) {

       print('Unknown error: $e!');

     }

     print('\nplease input the expression:');

     ins = stdin.readLineSync();

   }

 }