后缀表达式的计算

#include"seqlist.h"

template<class T, class Container> //适配器模式
class Stack
{
public:
Stack()
:_size(0)
{}
void Push(const T& x)
{
_con.PushBack(x);
_size++;

}
void Pop()
{
_con.PopBack();
_size--;

}
bool Empty() //判空
{
return _size == 0;
}
int size() //计算栈的长度
{
return _size;
}
T& top() //返回栈顶元素
{
return _con.top();
}

private:
Container _con;
size_t _size;
};

enum TYPE
{
OP_NUM,
ADD,
SUB,
MUL,
DIV,
};

struct Exp
{
TYPE _type;
int _data;
};

//中缀表达式 12 *（3 + 4）- 6 + 8 / 2
//后缀表达式 12 3 4 + * 6 - 8 2 / +
Exp RPN_Exp[] = {
OP_NUM, 12,
OP_NUM, 3,
OP_NUM, 4,
ADD ,0,
MUL, 0,
OP_NUM, 6,
SUB, 0,
OP_NUM, 8,
OP_NUM, 2,
DIV, 0,
ADD, 0,
};
Stack<int, SeqList<int>> s1;

int CountRPN_Exp(Exp* RPN_Exp,int size)
{
int left = 0, right = 0;
int res = 0;
for (int i = 0; i < size; i++)
{
switch((RPN_Exp + i)->_type)
{
case ADD:
right = s1.top();
s1.Pop();
left = s1.top();
s1.Pop();
res = left + right;
s1.Push(res);
break;
case SUB:
right = s1.top();
s1.Pop();
left = s1.top();
s1.Pop();
res = left - right;
s1.Push(res);
break;
case MUL:
right = s1.top();
s1.Pop();
left = s1.top();
s1.Pop();
res = left * right;
s1.Push(res);
break;
case DIV:
right = s1.top();
s1.Pop();
left = s1.top();
s1.Pop();
res = left / right;
s1.Push(res);
break;
case OP_NUM:
s1.Push((RPN_Exp + i)->_data);
break;
default:
cout << "无法计算" << endl;
}
}
return s1.top();
}

void test()
{
int ret = CountRPN_Exp(RPN_Exp, sizeof(RPN_Exp) / sizeof(RPN_Exp[0]));
cout <<ret;
}

int main()
{
test();
getchar();
return 0;
}

/*后缀表达式的计算过程：如果遇到操作数，则入栈。如果该项是操作符，则连续从栈中退出两个操作数
X和Y，形成运算指令X<op>Y，并将计算结果重新压入栈中，当表达式的所有想都扫描并处理之后，栈顶
存放的就是最后计算结果。*/