Count Characters in String C#

private int CountChar(string src, char x)
        {
            int count = 0;

            for (int i = 0; i < src.Length; i++)
            {
                //.ToString().ToUpper(): CaSe sensitive or not
                if (x.ToString().ToUpper() == src[i].ToString().ToUpper()) count++;
            }

            return count;
        }