二分查找

Position BinarySearch( List L, ElementType X )
{
    int p = 0;
    int left = 1;
    int right = L->Last;
    int mid;
    while(left<=right)
    {
        mid = (left + right) / 2;
        if(L->Data[mid] == X)//中间的数为被查数！！！
        {
            p = mid;
            break;
        }
        else if(L->Data[mid] > X)
        {
            right = mid-1;
        }
        else if(L->Data[mid] < X)
        {
            left = mid+1;
        }
        
    }
    if(p == 0)
        return NotFound;
    return p;
}