程序代码：

char a[4][4];
    //无法正确输入？？？
    while (cin >> a[1]) {
        cin >> a[2];
        cin>> a[3];
        cout << a[1][1] << a[3][3] << endl;
        if ( is(a)   )
            cout << "YES" << endl;
        else
            cout << "NO" << endl;
    }