求指出错误之处，可 不要代码

这是我的代码：

#include <string>
using namespace std;
struct node {
        int type;
        string ad;
} a[1005];
bool isAdCorrect(string ad) {
        int onep = 0;
        int twop = 0;
        int nlen = 0;
        int cnt = 1;
        int sum = 0;
        for (int i = ad.length() - 1; i >= 0; i--) {
                if (ad[i] >= '0' && ad[i] <= '9') {
                        nlen++;
                        sum += cnt * (ad[i] - '0');
                        cnt *= 10;
                } else if (ad[i] == '.') {
                        if (ad[i+1] == '0' && nlen > 1) {
                                return false;
                        }
                        if (sum > 255) {
                                return false;
                        }
                        if (twop < 1) {
                                return false;
                        }
                        onep++;
                        nlen = 0;
                        sum = 0;
                        cnt = 1;
                } else if (ad[i] == ':') {
                        if (ad[i+1] == '0' && nlen > 1) {
                                return false;
                        }
                        if (sum > 65535) {
                                return false;
                        }
                        if (onep > 0) {
                                return false;
                        }
                        twop++;
                        nlen = 0;
                        sum = 0;
                        cnt = 1;
                } else {
                        return false;
                }
        }
        if (onep != 3 || twop != 1) {
                return false;
        }
        return true;
}
int main() {
        int n;
        cin >> n;
        for (int i = 1; i <= n; i++) {
                string op;
                cin >> op;
                if (op == "Server") {
                        a[i].type = 0;
                        cin >> a[i].ad;
                        if (!isAdCorrect(a[i].ad)) {
                                cout << "ERR" << endl;
                                continue;
                        }
                        bool flag = true;
                        for (int j = 1; j < i; j++) {
                                if (a[j].type == 0 && a[j].ad == a[i].ad) {
                                        cout << "FAIL" << endl;
                                        flag = false;
                                        break;
                                }
                        }
                        if (!flag) {
                                continue;
                        }
                        cout << "OK" << endl;
                } else if (op == "Client") {
                        a[i].type = 1;
                        cin >> a[i].ad;
                        if (!isAdCorrect(a[i].ad)) {
                                cout << "ERR" << endl;
                                continue;
                        }
                        bool flag = false;
                        for (int j = 1; j < i; j++) {
                                if (a[j].type == 0 && a[j].ad == a[i].ad) {
                                        cout << j << endl;
                                        flag = true;
                                        break;
                                }
                        }
                        if (flag) {
                                continue;
                        }
                        cout << "FAIL" << endl;
                } else {
                        a[i].type = -1;
                        cin >> a[i].ad;
                }
        }
        return 0;
}