逆波兰表达式

 以输入正确的逆波兰表达式为前提，计算结果。。。

#define MAXSIZE 10
typedef struct Node
{
    double data;
    struct Node *next;
}Node;

typedef struct Stack
{
    Node *top;
}Stack;

void s_push(Stack *s, double data);
void s_pop(Stack *s, double *d);


int main()
{
    Stack s = {NULL};
    char l[MAXSIZE] = {0};
    char el;
    double d,e;
    int i = 0;
    
    printf("输入逆波兰表达式，以#结尾：
");
    scanf("%c", &el);
    
    while(el!='#')
    {
        if(isdigit(el) || el == '.')
        {
            l[i] = el;
            l[i+1] = '';
        }
        if(el == ' ')
        {
            if(l[0]) {
                s_push(&s, atof(l));
                l[0] = '';
                i = 0;
            }
            
        }
        
        switch(el)
        {
            case '+':
                s_pop(&s, &e);
                s_pop(&s, &d);
                s_push(&s, d+e);
                break;
            case '-':
                s_pop(&s, &e);
                s_pop(&s, &d);
                s_push(&s, d-e);
                break;
            case '*':
                s_pop(&s, &e);
                s_pop(&s, &d);
                s_push(&s, d*e);
                break;
            case '/':
                s_pop(&s, &e);
                s_pop(&s, &d);
                if(e == 0) {
                    printf("除数为0");
                    exit(-1); 
                }
                s_push(&s, d/e);
                break;
        }
        
        scanf("%c", &el);
    }
    
    s_pop(&s, &d);
    printf("计算结果：%f", d);
    
    return 0;
}

void s_push(Stack *s, double data)
{
    Node *p = (Node *)malloc(sizeof(Node));
    p->data = data;
    p->next = s->top;
    s->top = p;
}

void s_pop(Stack *s, double *d)
{
    Node *p = s->top;
    if(p == NULL)
    {
        return ;
    }
    *d = p->data;
    s->top = p->next;
    free(p);
    
}