解释器模式(interpretor)

 1 #include <iostream>
 2 #include <string>
 3 #include <vector>
 4 #include <stdio.h>
 5 using namespace std;
 6 
 7 //抽象的表达式对象以及Context对象
 8 //用于保存计算的中间结果以及当前执行的操作符
 9 class Context {
10 public:
11     int m_value;
12     char m_operator;
13     Context() :m_value(0), m_operator('\0') {
14 
15     }
16 };
17 //1+3-2
18 
19 //表示所有表达式的抽象接口
20 class IExpression {
21 public:
22     virtual void Eval(Context* p) = 0;
23 };
24 
25 //拆分表达式的元素
26 class Operator :public IExpression {
27 public:
28     Operator(char op) {
29         this->m_op = op;
30     }
31     void Eval(Context *pContext) {
32         pContext->m_operator = m_op;
33     }
34 private:
35     char m_op;
36 };
37 
38 //拆分操作数
39 class Operand :public IExpression {
40 public:
41     Operand(int num) {
42         this->m_num = num;
43     }
44     void Eval(Context* pContext) {
45         switch (pContext->m_operator)
46         {
47         case '\0':pContext->m_value = m_num;break;
48         case '+':pContext->m_value += m_num;break;
49         case '-':pContext->m_value -= m_num;break;
50         default:
51             break;
52         }
53     }
54 private:
55     int m_num;
56 };
57 
58 class Calculator {
59 public:
60     int Calc(string expression) {
61         Context* pCpontext = new Context;
62         vector<IExpression*> tree;
63         for (int i = 0;i < expression.size();i++) {
64             if ((expression[i] == '+') || (expression[i] == '-')) {
65                 tree.push_back(new Operator(expression[i]));
66                 printf("第%d次压入的符号是=%c\n", i, expression[i]);
67             }
68             else {
69                 tree.push_back(new Operand((int)(expression[i] - 48)));
70                 printf("第%d次压入的数字是=%d\n", i,((int)( expression[i]-48)));
71             }
72         }
73         for (vector<IExpression*>::iterator iter = tree.begin();iter != tree.end();iter++) {
74             (*iter)->Eval(pCpontext);
75             printf("value=%d,oper=%c\n", pCpontext->m_value, pCpontext->m_operator);
76         }
77         return pCpontext->m_value;
78     }
79 };
80 
81 int main(void) {
82     Calculator* pc = new Calculator;
83     cout << "1+4-2=" << pc->Calc("1+4-2") << endl;
84     system("pause");
85     return 0;
86 }