Why is my code wrong?

#1

i am taking input numbers as string;
and comparing them lexicographically;

bool cmp(string s1, string s2)
{
return s1 > s2;
}
int main()
{
int t;
cin >> t;

while (t--)
{
    int n;
    cin >> n;
    string s[n];
    for (int i = 0; i < n; i++)
    {
        cin >> s[i];
    }
    sort(s, s + n, cmp);
    for (int i = 0; i < n; i++)
    {
        cout << s[i];
    }

}

}

#2

@rajdev1409 your compartor function logic is incorrect

// first append Y at the end of X
    string XY = X.append(Y);

    // then append X at the end of Y
    string YX = Y.append(X);

    // Now see which of the two formed numbers is greater
    return XY.compare(YX) > 0 ? 1: 0;
#3

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