大数相加

大数相加（A+B）

这是一道很简单基础的面试题，大数相加转换成字符串处理即可

• 获取A,B的长度

• 字符串反序

• 进位处理

---

字符串反向

char *reverse_str(char *a) {
    if(a == NULL)
        return NULL;
    int len = strlen(a);
    char *left = a;
    char *right = a + len - 1;
    while(left < right) {
        *left  ^= *right;
        *right ^= *left;
        *left  ^= *right;
        if(left == (right - 1)) {
            break;
        }
        left++;
        right--;
    }
    return a;
}

相加处理

char* add(char *a, char *b) {
    int len = strlen(a);
    int len_b = strlen(b);
    char ans[100];
    memset(ans, 0, sizeof(ans));
    len > len_b ? len : len_b;
    reverse_str(a);
    reverse_str(b);
    int i = 0, ret = 0, flag = 0;
    int tmp;
    while(i < len && flag == 0) {
        if(a[i] < '0' || a[i] > '9') {
            flag = 1;
            break;
        } else if(b[i] < '0' || b[i] > '9') {
            flag = 2;
            break;
        }
        tmp = (a[i] - '0') + (b[i] - '0') + ret;
        ans[i] += (tmp % 10) + '0';
        ret = tmp / 10;
        i++;
    }
    if(flag == 1) {
        for(i; i < len; i++) {
            tmp = (b[i] - '0') + ret;
            ans[i] += (tmp % 10) + '0';
            ret = tmp / 10;
        }
    } else if(flag == 2) {
        for(i; i < len; i++) {
            tmp = (a[i] - '0') + ret;
            ans[i] += (tmp % 10) + '0';
            ret = tmp / 10;
        }
    }
    if(ret != 0)
        ans[i] = ret + '0';

    reverse_str(ans);

    cout << ans;
}

主函数

int main() {
    char a[100];
    char b[100];
    cin >> a;
    cin >> b;
    add(a, b);
    return 0;
}