Binary Search  From Astrachan p 392
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int WordList::Search(string key)
// postcondition: returns index at which key occurs in myList
//                returns -1 if key does not occur     
{
    int low = 0;
    int high = myCount-1;
    int mid;                          // middle of current range
    while (low <= high)
    {
        mid = (low + high)/2;
        if (myList[mid] == key)       // found key, exit search
        {
            return mid;
        }
        else if (myList[mid] < key)   // key in upper half
        {
            low = mid + 1;
        }
        else                          // key in lower half
        {
            high = mid - 1;
        }
    }
    return -1;			      // not in list
}