四則運算

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#define max 100
char tab[max];
int i=0;
double caculate(char c ,double a,double b)
{
    double j=0,ans=a;
    switch(c)
    {
        case '+': return a+b;
        case '-': return a-b;
        case '*': return a*b;
        case '/': return a/b;
        case '^':
                for(j=1;j<b;j++)
                    ans*=a;
                return ans;
    }
}
int jude(char a)
{
    if(a=='^')return 2;
    else if(a=='*'||a=='/') return 1;
    else return 0;
}
double caculate_op()
{
    int top=-1,n=0,j,k;
    char stack_op[max];
    double stack_number[max],number;
    double number_double;
    double used[max]={0};
    while(1)
    {
        number=0;
        number_double=0;
        if(tab[i]>='0'&&tab[i]<='9')
        {
            do
             {
                number=number*10+tab[i]-48;
                i++;
             } while(tab[i]>='0'&&tab[i]<='9');
             if(tab[i]=='.')
            {
                i++;
                double count=1,temp;
                do
                 {
                     temp=tab[i]-48;
                     for(j=0;j<count;j++)
                        temp/=10.0;
                     number_double+=temp;
                     i++;
                     count++;
                 } while(tab[i]>='0'&&tab[i]<='9');
            }
             i--;
            number+=number_double;
            stack_number[n]=number;
            n++;
        }
        else
            switch(tab[i])
            {
                case '\0':
                case ')' :
                         for(j=2;j>=0;j--)
                         {
                             for(k=0;k<=top;k++)
                                 if(jude(stack_op[k])==j)
                                 {
                                     int count=0;
                                     while(used[k-count]==-1){count++;}
                                     stack_number[k-count]=caculate(stack_op[k],stack_number[k-count],stack_number[k+1]);
                                     stack_number[k+1]=0;
                                     used[k+1]=-1;
                                 }
                         }
                         for(j=0;j<n;j++)
                             number+=stack_number[j];
                         return number;
                 case '(' :
                         i++;
                         stack_number[n]=caculate_op();
                         n++;
                         break;
                 default :
                    top++;
                    stack_op[top]=tab[i];
                   break;
             }
        i++;
    }
}
int main()
{
    scanf("%s", tab);
    printf("%lf\n",caculate_op());
    return 0;
}