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();
  }
}