Dijkstra的双栈算术表达式求值算法 C++实现

 #include<iostream>
 #include<string>
 using namespace std;

 template<typename T>
 class Stack
 {
 private:
     T stack[];
     int i = ;
 public:
     Stack() = default;

     T pop()
     {
         if (i == -)
         {
             cout << "栈已空！" << endl;
             return ;
         }

         T top = stack[i - ];
         --i;
         return top;
     }

     void push(T num)
     {
         ++i;
         stack[i - ] = num;
     }

     void clear()
     {
         for (int j = ; j < ; ++j)
         {
             T[j] = ;
         }
     }
 };

 int main()
 {
     Stack<string> ops;
     Stack<double> num;
     string str;

     std::cout << "请输入计算式： " << endl;
     cout << "注： 每个字符间请以空格分开，子表达式请用括号括起注明" << endl;
     cout << "字符 E 代表结束" << endl;
     while (true)
     {
         cin >> str;
              if (str == "(")      continue;
         else if (str == "+") ops.push(str);
         else if (str == "-") ops.push(str);
         else if (str == "*") ops.push(str);
         else if (str == "/") ops.push(str);
         else if (str == ")")
         {
             string op = ops.pop();
             double val = num.pop();
             if (op == "+") val = num.pop() + val;
             if (op == "-") val = num.pop() - val;
             if (op == "*") val = num.pop() * val;
             if (op == "/") val = num.pop() / val;
             num.push(val);
         }

         else if (str != "E")
         {
             double val = stod(str);
             num.push(val);
         }

         if (str == "E")
         {
             break;
         }
     }

     cout << "结果为： ";
     cout << num.pop() << endl;

     return ;
 }