Get Count of Occurrence of Characters in String using C#

public void CharCount()
{
    string str = Console.ReadLine();
    int length = str.Length;
    char[] charArr = new char[length];
    for (int i = 0; i < length; i++)  //Converting String to Char Array
    {
        charArr[i] = str[i];
    }

    for (int i = 0; i < length; i++)
    {
        bool flag = false;
        for (int k = i - 1; k >= 0; k--)      //Checking whether the current char already repeated or not
        {
            if (char.ToUpper(charArr[i]) ==char.ToUpper(charArr[k]))
            {
                flag = true;
            }
        }
        if (!flag)
        {
            int count = 1;
            for (int j = i+1; j < length; j++)
            {
                if (char.ToUpper(charArr[i]) ==char.ToUpper(charArr[j]))
                {
                    count++;
                }
            }
            Console.WriteLine(char.ToLower(charArr[i]) + "=" + count);
        }
    }
}