2D ArrayList Binary Search c#

Question

Been asked to create a binary search method for a 2D array that sorts through strings. I'm doing as part of a course that has lots of specifics, i can't use any pre-built search methods but i have to create this without any learning content, all I've been provided is a standard Binary search method for a 1D array containing Integers, so not much help.

        private void BtnSearch_Click(object sender, EventArgs e)
        {

            int startIndex = 0;
            int finalIndex = gameArray.Length -1;

            bool flag2 = false;
            string searchTerm = txtSearch.Text;
            int foundIndex = -1;


            while (!flag2 && !((finalIndex - startIndex) <= 1))
            {
                int middle = (finalIndex + startIndex) / 2;
                if (string.Compare(gameArray[middle, 0], searchTerm, true) == 0)
                {
                    foundIndex = middle;
                    flag2 = true;
                    break;
                }
                else
                {
                    if (string.Compare(gameArray[middle, 0], searchTerm, true) > 0)
                        finalIndex = middle;
                    else
                        startIndex = middle;
                }

            }
            if (flag2)
                lstGames.SelectedIndex = foundIndex;
            else
                MessageBox.Show("Not Found");

        }

I keep getting this error message any time i execute the search in the program.

System.IndexOutOfRangeException: 'Index was outside the bounds of the array.'

Which happens on the While loops execution

Really not too sure what I'm doing incorrect at this point.

Answer 1

You should check if "middle" is equal or greater than length of the array before test.

Avoid use !((finalIndex-startIndex)<=1) when you have (finalIndex-startIndex> 1). So much clean.

!flag2 is unnecessary in while clause because only breaks after flag2 is true;

Edit: you aren't solving the index offset problems. Take a look at this BS basic loop

int minIndex=0;
int maxIndex=data.Length-1;

while (minIndex <=maxIndex) { //this is the only control you have to do
  int mid = (minIndex + maxIndex) / 2;
  if (key == data[mid]) { //compare, or do stuff
     return ++mid;
  } else if (key < data[mid]) { //compare or do stuff
     maxIndex = mid - 1; //this -1 is important in performance
  }else {
     minIndex = mid + 1; //this +1 is important in performance
  }
}

And i recommend you follow SRP (Single responsability bla bla). Make "BinarySearch" a standalone method, and make it return found index or -1 if not found, and use that method where you want. You can make it even generic.