1.3.2.4 怎么做

#include <cstdio>
const int MAX = 100001;
int stack[MAX / 2] = { 0 };
char abcd[MAX] = { 0 }, strsta[MAX / 2] = { 0 };
int len = 0, lens = 0, lenr = 0;
int main() {
    int tmp = 0;
    char c = getchar();
    while (c != '\n') {
        abcd[len++] = c;
        c = getchar();
    }
    for (int i = 0; i < len; i++) {
        if (abcd[i] >= '0' && abcd[i] <= '9') {
            tmp *= 10;
            tmp += abcd[i] - '0';
        } else {
            if (abcd[i - 1] != ')')
                stack[lens++] = tmp;
            tmp = 0;
            strsta[lenr++] = abcd[i];
            if (abcd[i] == ')') {
                int j = lenr - 1;
                while (strsta[j] != '(') j--;
                if (strsta[lenr - 2] == '*') {
                    stack[lens - 2] *= stack[lens - 1];
                    lens--;
                }
                if (strsta[lenr - 2] == '/') {
                    if (stack[lens - 1] == 0) {
                        printf("div0.");
                        return 0;
                    }
                    stack[lens - 2] /= stack[lens - 1];
                    lens--;
                }
                stack[j] = stack[j + 1];
                for (int k = j + 1; k < lenr - 1; k++) {
                    if (strsta[k] == '+')
                        stack[j] += stack[k + 1];
                    if (strsta[k] == '-')
                        stack[j] -= stack[k + 1];
                    strsta[k] = stack[k + 1] = 0;
                }
                strsta[j] = 0;
                lenr = j;
                lens = j + 1;
            }
        }
        if (i == len - 1 && abcd[i] <= '9' && abcd[i] >= '0')
            stack[lens++] = tmp;
        if (strsta[lenr - 2] == '*' && strsta[lenr - 1] != '(') {
            stack[lens - 2] *= stack[lens - 1];
            strsta[lenr - 2] = strsta[lenr - 1];
            lens--;
            lenr--;
        }
        if (strsta[lenr - 2] == '/' && strsta[lenr - 1] != '(') {
            if (stack[lens - 1] == 0) {
                printf("div0.");
                return 0;
            }
            stack[lens - 2] /= stack[lens - 1];
            strsta[lenr - 2] = strsta[lenr - 1];
            lens--;
            lenr--;
        }
    }
    if (strsta[lenr - 1] == '*') {
        stack[lens - 2] *= stack[lens - 1];
        lens--;
    }
    if (strsta[lenr - 1] == '/') {
        if (stack[lens - 1] == 0) {
            printf("div0.");
            return 0;
        }
        stack[lens - 2] /= stack[lens - 1];
        lens--;
    }
    for (int i = 0; i < lens; i++) {
        if (strsta[i] == '+')
            stack[0] += stack[i + 1];
        if (strsta[i] == '-')
            stack[0] -= stack[i + 1];
    }
    printf("%d", stack[0]);
    return 0;
}