using System;

public class Program

{

    public static void Main()

    {

        int[] breakpoint = new int[] {0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100,

         110, 120, 130, 140, 150, 160, 170, 180, 190, 200};

        foreach(int valueSearched in new[]{153, 225, -1, 5})

        {

            int index = GetNearestIndex(breakpoint, valueSearched);

            Console.WriteLine($"Searched <{valueSearched}> at index <{index}> with value <{breakpoint[index]}>");

        }

    }

    public static int GetNearestIndex<T>(T[] items, T value)

    {

        int index = Array.BinarySearch(items, value);

        if(index >= 0) 

            return index;

        if(index == -1)

            return 0;

        return ~index - 1;

    }

}

​

​