private int BinarySearch(double[] array, double value)
{
    if (array == null || array.Length <= 0) return -1;
    int low = 0;
    int hi = array.Length - 1;
    while (low <= hi)
    {
        int m = low + ((hi - low) >> 1); // 中间值
        if (value > array[m])
            low = m + 1;
        else hi = m - 1;
    }
    low = Math.Min(low, array.Length - 1);
    if (low <= 0) return low;
    else return value - array[low - 1] < array[low] - value ? low - 1 : low;
}

private void button1_Click(object sender)
{
    double[] A = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    //Array.Sort(A);//初始化，之后可以顺序插入
    double[] B = { 1, 2, 2.5, 3.51, 3.49, 9, 100};
    for (int i = 0; i < B.Length; i++)
    {
        int j = BinarySearch(A, B[i]);
        Console.WriteLine("B={0},Index:{1},Value:{2}", B[i], j, j < 0 ? -1 : A[j]);
    }
}

double[] A = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
//Array.Sort(A);//初始化，之后可以顺序插入
double[] B = { 1, 2, 2.5, 3.51, 3.49, 9, 100};
for (int i = 0; i < B.Length; i++)
{
    IEnumerable<double> query =
        from student in A
        orderby Math.Abs(student - B[i])
        select student;
    Console.WriteLine("B={0},Value:{1}", B[i], query.First<double>());
}