四则运算表达式求值 OpenJ_Bailian - 4132

  1 #include <bits/stdc++.h>
  2 using namespace std;
  3 const int maxn=10010;  //最大表达式长度
  4 
  5 template <typename T>
  6 class Stack;
  7 
  8 template <typename T>
  9 class Node{
 10     friend Stack<T>;
 11 private:
 12     T x;
 13     Node<T> *nxt;
 14 };
 15 
 16 template <typename T>
 17 class Stack{
 18 public:
 19     Stack() {head=NULL;}
 20     virtual ~Stack(){if(head) delete head;}
 21     virtual void init() {head=NULL;}
 22     virtual bool _empty() const {return head==NULL;}
 23     virtual T top() const;
 24     virtual void pop();
 25     virtual void push(const T a);
 26 private:
 27     Node<T> *head;
 28 };
 29 
 30 template <typename T>
 31 T Stack<T>::top() const{
 32     return head->x;
 33 }
 34 
 35 template <typename T>
 36 void Stack<T>::pop(){
 37     head=head->nxt;
 38 }
 39 
 40 template <typename T>
 41 void Stack<T>::push(const T a){
 42     Node<T>  *tmp=new Node<T>();
 43     tmp->x=a;
 44     tmp->nxt=head;
 45     head=tmp;
 46 }
 47 
 48 char s[maxn];
 49 Stack<char> op;
 50 Stack<double> num;
 51 void cal(){
 52     double x=num.top();num.pop();
 53     double y=num.top();num.pop();
 54     char c=op.top();op.pop();
 55     switch(c){
 56     case ‘+‘:
 57         num.push(x+y);
 58         break;
 59     case ‘-‘:
 60         num.push(y-x);
 61         break;
 62     case ‘*‘:
 63         num.push(x*y);
 64         break;
 65     case ‘/‘:
 66         num.push(y/x);
 67         break;
 68     }
 69     return ;
 70 }
 71 bool check(char c1,char c2){
 72     int a,b;
 73     double x=num.top();num.pop();
 74     if(num._empty()) {num.push(x); return 0;}
 75     else num.push(x);
 76 
 77     switch (c1){
 78         case ‘+‘: a=0;break;
 79         case ‘-‘: a=0;break;
 80         case ‘*‘: a=1;break;
 81         case ‘/‘: a=1;break;
 82         case ‘(‘: a=-1;break;
 83     }
 84     switch (c2){
 85         case ‘+‘: b=0;break;
 86         case ‘-‘: b=0;break;
 87         case ‘*‘: b=1;break;
 88         case ‘/‘: b=1;break;
 89     }
 90     return a>=b;
 91 }
 92 
 93 int main(){
 94     while(cin>>s){
 95         op.init();
 96         num.init();
 97         int len=strlen(s);
 98         for(int i=0;i<len;i++){
 99             if(isdigit(s[i])) {
100                 double x=atof(&s[i]);
101                 while(i<len&&(s[i+1]==‘.‘||isdigit(s[i+1]))) i++;
102                 num.push(x);
103             }
104             else{
105                 if(s[i]==‘(‘){
106                     op.push(s[i]);
107                 }else if(s[i]==‘)‘){
108                     while(!op._empty()&&op.top()!=‘(‘){
109                         cal();
110                     }
111                     op.pop();
112                 }else if(s[i]==‘=‘){
113                     while(!op._empty())
114                         cal();
115                 }else if(op._empty()){
116                     op.push(s[i]);
117                 }else {
118                     while(!op._empty()&&check(op.top(),s[i])){
119                         cal();
120                     }
121                     op.push(s[i]);
122                 }
123 
124             }
125         }
126         while(!op._empty()) cal();
127         printf("%.2lf\n",num.top());
128     }
129     return 0;
130 }