Execise2

static void SwapDiagMaxMin(int[,] arr, int len)
        {
            int max, min;
            for (int i = 0; i < len; i++)
            {
                max = min = arr[i, 0];
                for (int j = 0; j < len; j++)
                {
                    if (arr[i, j] > max) { max = arr[i, j]; }
                    if (arr[i, j] < min) { min = arr[i, j]; }
                }
                tmp = arr[i, i];
            arr[i, i] = arr[iMax, jMax];
            arr[iMax, jMax] = tmp;
            tmp = arr[i, len - i - 1];
            arr[i, len - i - 1] = arr[iMin, jMin];
            arr[iMin, jMin] = tmp;
            }
        }