栈的应用之后缀表达式

#include<iostream>  #include<stack>using namespace std;enum Type{_SYMBOL,  //操作符  _NUM,      //操作数  ADD,SUB,MUL,DIV,};struct Cell{Type _type;     //每个传进来的单元的类型  int _value;    //操作数  };int CountRPN(Cell* rpn, size_t n){stack<int> s;for (size_t i = 0; i<n; i++){//判断传进来的是操作符还是操作数压栈if (_NUM == rpn[i]._type){s.push(rpn[i]._value);}if (_SYMBOL == rpn[i]._type){int right = s.top();s.pop();int left = s.top();s.pop();            //是操作符，就进行四则运算switch (rpn[i]._value){case 2:s.push(left + right);break;case 3:s.push(left - right);break;case 4:s.push(right*left);break;case 5:if (right == 0)    //抛异常  {throw std::invalid_argument("参数错误！");//invalid_argument非法的参数，也是标准异常，  }s.push(left / right);break;default:throw std::invalid_argument("参数异常");break;}}}return s.top();}void Test(){       //原来的式子是：17  //转换成后缀表达式：12 3 4 * -5 - 2 +Cell Rpn[] = {{ _NUM,  },{ _NUM, 3 },{ _NUM, 4 },{ _SYMBOL, MUL },{ _SYMBOL, SUB },{ _NUM, 5 },{ _SYMBOL, SUB },{ _NUM, 2 },{ _SYMBOL, ADD },};try{cout << CountRPN(Rpn, sizeof(Rpn) / sizeof(Rpn[0])) << endl;}catch (exception&e)   //捕获异常  {e.what();cout << "error" << endl;}}int main(){Test();system("pause");return 0;}