using System;

using System.Collections.Generic;

public class Program

{

    public char? CheckMaxOccuranceOfChar(string givenstring)

    {

        char? maxOccuranceChar = null;  

        int maxOccuranceValue = 0;

        if(string.IsNullOrEmpty(givenstring))

        return null;

        givenstring = givenstring.ToLower().Trim();

        char[] arr = givenstring.ToCharArray();

        Dictionary<char, int> _dictionary = new Dictionary<char, int>();

        for(int i = 0; i < arr.Length; i++)

        {

            if(arr[i] != ' ')

            {

                if(! _dictionary.ContainsKey(arr[i]))

                {

                    _dictionary.Add(arr[i],1);

                }

                else

                {

                    _dictionary[arr[i]]++;  

                }

            }

        }

​

        foreach (KeyValuePair<char, int> item in _dictionary)  

            {  

                if (item.Value > maxOccuranceValue)  

                {  

                    maxOccuranceChar = item.Key;  

                    maxOccuranceValue = item.Value;  

                }  

            }  

            return maxOccuranceChar; 

    }

    public static void Main()

    {

        Program p = new Program();

        var finalresult = p.CheckMaxOccuranceOfChar("Hello World");

        Console.WriteLine("Max occurrence of a character in the string is : " + finalresult);

    }

}