请输入行列数量:9
1 0 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 0
0 0 0 1 0 0 0 0 0
0 0 0 0 1 0 0 0 0
0 0 0 0 0 1 0 0 0
0 0 0 0 0 0 1 0 0
0 0 0 0 0 0 0 1 0
0 0 0 0 0 0 0 0 1

int N = 0;
cout << "请输入行列数量:";
cin >> N;
for (int i = 1; i < N + 1; i++) {
    for (int j = 1; j < N + 1; j++)
        if (________) // 此处填写代码
            cout << 1 << " ";
        else
            cout << 0 << " ";
    cout << endl;
}