C++之面向对象版表达式计算器（一）

1、常规

Node.h

class Node {
public:
    virtual double Calc() const = 0;
    virtual ~Node() {};
};

class NumberNode : public Node
{
public:
    NumberNode(double number) : number_(number)
    {

    }
    double Calc() const;
private:
    const double number_;
};

class BinaryNode : public Node
{
public:
    BinaryNode(Node* left, Node* right):left_(left), right_(right)
    {}

    ~BinaryNode();

protected:
    Node* const left_;  // const在*右边，表示指针不能再指向别的节点了
    Node* const right_;
};

// 加法
class AddNode : public BinaryNode
{
    AddNode(Node* left, Node* right) : BinaryNode(left, right)
    {
    }

    double Calc() const;
};

// 减法
class SubNode : public BinaryNode
{
    SubNode(Node* left, Node* right) : BinaryNode(left, right)
    {
    }

    double Calc() const;
};

// 乘法
class MultiplyNode : public