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 }
