//一个简单的计算器代码，主要用来练习C++11新标准的编程技术和stl应用
  1 #include<iostream>
  2 #include<stack>
  3 #include<map>
  4 #include<set>
  5 #include<functional>
  6 #include<string>
  7 using namespace std;
  8 
  9 
 10 typedef function<float(float,float)> optionFun;
 11 stack<float> snumber;
 12 stack<string> soption;
 13 map<string,optionFun> optFunMap;
 14 map<string,int> optWeightMap;
 15 
 16 #define DECLARE_OPT(opts,preority)  17     optWeightMap[#opts] = int(preority); 18     optFunMap[#opts] = bind([](float a, float b){return a opts b;}, placeholders::_1, placeholders::_2);
 19 
 20 
 21 void init_option()
 22 {
 23     DECLARE_OPT(+,1);
 24     DECLARE_OPT(-,1);
 25     DECLARE_OPT(*,2);
 26     DECLARE_OPT(/,2);
 27 }
 28 
 29 bool isoption(string op)
 30 {
 31     auto it = optWeightMap.find(op);
 32     return it!=optWeightMap.end();
 33 }
 34 float recognize_float(const char* pstr, int& width)
 35 {
 36     char value[24]={0};
 37     int dotcount = 0;
 38     for(int i=0;pstr[i]!=‘\0‘;i++)
 39     {
 40         int x = pstr[i];
 41         if(isdigit(x)||(x==‘.‘&&dotcount==0))
 42         {
 43             value[i] = x;
 44             dotcount++;
 45         }
 46         else
 47         {
 48             width = i;
 49             break;
 50         }
 51     }
 52     return atof(value);
 53 }
 54 
 55 //offset from ‘(‘ to ‘)‘
 56 int check_match(const char* str)
 57 {
 58     int offset = 1;
 59     bool match = false;
 60     while(str[offset]!=‘\0‘)
 61     {
 62         if(str[offset++]==‘)‘)
 63         {
 64             match = true;
 65             break;
 66         }
 67     }
 68     return match?offset:-1;
 69 }
 70 
 71 void handle_stack()
 72 {
 73     while(!soption.empty())
 74     {
 75         string opt = soption.top();
 76         if(opt=="(") 
 77         {
 78             soption.pop();
 79             break;
 80         }
 81         auto it = optFunMap.find(opt);
 82         if(it != optFunMap.end())
 83         {
 84             auto fun = it->second;
 85             float a= snumber.top();
 86             snumber.pop();
 87             float b = snumber.top();
 88             snumber.pop();
 89             snumber.push(fun(b,a));
 90             soption.pop();
 91         }
 92     }
 93 }
 94 float calc(const char* str)
 95 {
 96     if(str==nullptr)
 97     {
 98         cout<<"invalid express"<<endl;
 99         return 0;
100     }
101 
102     if(*str==‘+‘||*str==‘-‘)
103     {
104         snumber.push(0);
105     }
106     while(*str!=‘\0‘)
107     {
108         if(isdigit(*str))
109         {
110             int len;
111             snumber.push(recognize_float(str,len));
112             str+=len;
113             continue;
114         }
115         if(*str==‘(‘)
116         {
117             int len = check_match(str);
118             if(len==-1)
119             {
120                 cout<<"sync error : the express less a ‘)‘"<<endl;
121                 return;
122             }
123             soption.push("(");
124             calc(str+1);
125             str += len;
126             continue;
127         }
128         if(*str==‘)‘)
129         {
130             handle_stack();
131             return 0;
132         }
133         string ops(1,*str);
134         if(isoption(ops))
135         {
136             if(!soption.empty())
137             {
138                 if(optWeightMap[ops]<optWeightMap[soption.top()])
139                 {
140                     handle_stack();
141                 }
142             }
143             soption.push(ops);
144             str++;
145             continue;
146         }
147         cout<<"invalid express"<<endl;
148         return 0;
149     }
150     handle_stack();
151     return snumber.top();
152 }
153 int main()
154 {
155     init_option();
156     string str;
157     while(str!="exit")
158     {
159         cout<<"> ";
160         cin>>str;
161         if("exit"==str)break;
162         cout<<calc(str.c_str())<<endl;
163     }
164     return 0;
165 }