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 }