表达式求值

 1 #include<stdio.h>   
 2 #include<string.h>   
 3 #include<stdlib.h>   
 4 char str[1005];  
 5 int start;  
 6 char s[50],ss[50];int i,j;  
 7 double Term();double Expression();double Factor();  
 8 double Term()  
 9 {  
10     double f=Factor(),t;  
11     --start;  
12     if(str[start]=='*')  
13     {  
14         t=Term();  
15         return t*f;  
16     }  
17     else if(str[start]=='/')  
18     {  
19         t=Term();  
20         return t/f;  
21     }  
22     else {++start;return f;}  
23 }  
24 double Expression()  
25 {  
26     double t=Term(),e;  
27     --start;  
28     if(str[start]=='+')  
29     {  
30         e=Expression();  
31         return e+t;  
32     }  
33     else if(str[start]=='-')  
34     {  
35         e=Expression();  
36         return e-t;  
37     }  
38     else {++start;return t;}  
39 }  
40 double Factor()  
41 {  
42     --start;  
43     double ret;  
44     if(str[start]==')')  
45     {  
46         ret=Expression();  
47         --start;  
48         return ret;  
49     }  
50     else  
51     {  
52         i=0;  
53         memset(ss,0,sizeof(ss));  
54         while((str[start]>='0'&&str[start]<='9')||str[start]=='.')  
55             s[i++]=str[start--];  
56         ++start;  
57         for(j=0;j<i;j++)  
58         {  
59             ss[j]=s[i-1-j];  
60         }  
61         return atof(ss);  
62     }  
63 }  
64 int main()  
65 {  
66     //freopen("1.txt","r",stdin);   
67     int n;  
68     scanf("%d",&n);  
69     while(n--)  
70     {  
71         scanf("%s",str);  
72         start=strlen(str)-1;  
73         printf("%.2lf\n",Expression());  
74     }  
75 }