表达式求值 NYOJ

#include<stdio.h>  
#include<stdlib.h>  
#include<string.h>  
  
char str[1005];  
char changestr[2010];  
double stack_n[1005];  
char stack_c[1005];  
int count_c = -1;  
int count_n = -1;  
  
  
char pop_c(){  
    return stack_c[count_c--];  
}  
  
char top_c(){  
    if(-1 == count_c)  
    return 0;  
    return stack_c[count_c];  
}  
  
void push_c(char t){  
    stack_c[++count_c]=t;  
}  
  
double top_n(){  
    if(-1 == count_n)  
    return 0;  
    return stack_n[count_n];  
}  
  
double pop_n(){  
    return stack_n[count_n--];  
}  
  
void push_n(double t){  
    stack_n[++count_n]=t;  
}  
  
int level(char ch){  
    switch(ch)  
    {  
    case '+':  
    case '-':return 1;  
    case '*':  
    case '/':return 2;  
    default:  
        return 0;  
    }  
}  
  
void change()  
{  
    int i;  
    int j=0;  
    for(i=0; i<strlen(str);)  
    {  
        switch(str[i])  
        {  
        case '(':push_c('(');i++;break;  
        case ')':  
            while(top_c()!='('&&count_c!=-1)  
            {  
                changestr[j++] = pop_c();  
                changestr[j++] = ' ';  
            }  
            pop_c();  
            i++;break;  
        case '+':  
        case '-':  
        case '*':  
        case '/':  
            while(level(str[i])<=level(top_c()))  
            {  
                changestr[j++] = pop_c();  
                changestr[j++] = ' ';  
            }  
            push_c(str[i]);  
            i++;break;  
        case '=':i++;break;  
        default:  
            {  
                while(str[i]<='9'&&str[i]>='0'||str[i]=='.')  
                    changestr[j++] = str[i++];  
                changestr[j++] = ' ';  
            }  
        }  
    }  
    while(count_c!=-1)  
    {  
        changestr[j++] = pop_c();  
        changestr[j++] = ' ';  
    }  
}  
  
double result(){  
    int i;  
    int len = strlen(changestr);  
    double x;  
    double y;  
    for(i=0; i<len; i++)  
    {  
        switch(changestr[i])  
        {  
            case '+':x = pop_n();x += pop_n();i++;break;  
            case '-':x = pop_n();x = pop_n()-x;i++;break;  
            case '*':x = pop_n();x *= pop_n();i++;break;  
            case '/':x = pop_n();x = pop_n()/x;i++;break;  
            default:  
                x = 0;  
                while(changestr[i]<='9'&&changestr[i]>='0')  
                {  
                    x= x*10 + changestr[i] - '0';  
                    i++;  
                }  
                if(changestr[i] == '.')  
                {  
                    double k = 10.0;  
                    y = 0;  
                    i++;  
                    while(changestr[i]<='9'&&changestr[i]>='0')  
                    {  
                        y+=((changestr[i]-'0')/k);  
                        i++;  
                        k*=10;  
                    }  
                    x+=y;  
                }  
        }  
        push_n(x);  
    }  
    return top_n();  
}  
  
int main()  
{  
    int n;  
    scanf("%d",&n);  
    getchar();  
    while(n--)  
    {  
        count_c = -1;  
        count_n = -1;  
        scanf("%s",str);  
        change();  
        printf("%.2f\n",result());  
    }  
    return 0;  
}