C# binary tree loop trouble

Question

I'm making a loop for searching a value from the array. If I find it, the position will be printed, if it's not "no such number" will be printed. But, if I have several same numbers, I will receive only one and then I am over the loop. How can I get the control, if the same number in the array? My best tries end with endless loop or completed loop from the start.

static public void Searching(int[] arr)
{
    string x = "yes";

    Console.WriteLine("Enter please searching number");
    while (x == "yes")
    {
        bool found = false;
        int target = Convert.ToInt32(Console.ReadLine());
        int searchkey = target;
        int mid = 0, first = 0, last = arr.Length - 1;
        while (!found && first <= last)
        {
            mid = (first + last) / 2;

            if (target == arr[mid])
                found = true;


            else
            {
                if (target > arr[mid])
                {
                    first = mid + 1;
                }

            if (target < arr[mid])
            {
                last = mid - 1;
            }
        }
    }
    String foundmsg = found
                ? "Item " + searchkey + " was found at position " + mid
                : "Item " + searchkey + " was not found";
    Console.WriteLine(foundmsg);
    Console.WriteLine("would you like to find another number?");
    x = Console.ReadLine();

        }

    }

Answer 1

Don't loop this. C# has built in functions to help you.

static public void Searching(int[] arr)
    {
        string x = "yes";

        Console.WriteLine("Please enter a number for which to search...");
        int target = Convert.ToInt32(Console.ReadLine());

        string Response = "Result of search is:"
        +  arr.IndexOf(target) != -1 
        ? arr.IndexOf(target).ToString() : "Not Found";
       //indexOf finds the first index of obj. in array
        Console.WriteLine(Response);
     }

This should satisfy your "when I find one of multiples I receive only one" requirement. You'll always get the first occurrence.

If you need all instances, and use a loop, it's not all that different.

static public void Searching(int[] arr)
    {
        string x = "yes";

        Console.WriteLine("Please enter a number for which to search...");
        int target = Convert.ToInt32(Console.ReadLine());
        string result = string.Empty
        for(int i =0; i < arr.Length; i++)
              if (i = target)
              { result += i.ToString() + ", " }
        }
        if(result != string.Empty)
        {
           result = result.SubString(0, result.Length - 2);
           //removes extra space and colon
        } else {
           result = "Not Found";
        }
        Console.WriteLine("Result of search is:"
        + result);
     }

Answer 2

If you're looking to return all of the positions in the array where a particular value is found then create a list (like List<int>) and as you find the number in the array, add the position to the list. That way you can search the entire array without breaking out of your loop.

Then when you're done executing there will be either one or more items in the list or the list will be empty. If there are items in the list display those. If there are no items in the list return the "not found" message.

For example,

var indexes = new List<int>();
for(var index = 0; index < source.Length; index++)
{
    if(source[index] == target) indexes.Add(index);
}

When you're done you'll have either a list of matches or an empty list.

Lots of nested loops can get confusing. You have an outer loop that's handling the Console inputs. One way to make that easier to read is to isolate part into a function. For example,

List<int> GetIndexesOfMatchingNumbers(int[] source, int target)
{
    var indexes = new List<int>();
    for(var index = 0; index < source.Length; index++)
    {
        if(source[index] == target) indexes.Add(index);
    }
}

You can call this function from your "main" function. It's functionally exactly the same but it reduces the amount of logic you have to follow when you read the code. That makes it easier to understand, even for the person writing it.

Answer 3

You can try using Array.BinarySearch in order to find some item's index and then starting from the index move backward and forward:

  int[] source = new[] { 1, 2, 3, 4, 4, 4, 4, 5, 15, 20 };

  int searchkey = 4;

  int first = -1;
  int last = -1;

  int index = Array.BinarySearch(source, searchkey);

  if (index >= 0) {
    first = index;
    last = index;

    for (int i = index - 1; i >= 0; --i)
      if (source[i] != toFind)
        break;
      else
        first = i;

    for (int i = index + 1; i < source.Length; ++i)
      if (source[i] != toFind)
        break;
      else
        last = i;

    if (first == last)
      Console.Write($"{searchkey} found at {first} position");
    else
      Console.Write($"{searchkey} found at [{first}..{last}] positions");
  }
  else
    Console.Write($"{searchkey} is not found");