Count the number of occurrences of the characters in a text, with ASP.NET C #

The example allows you to count the number of occurrences of the characters in a text.

Code:

/// <summary>
/// Count the number of occurrences of the characters in a text.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
protected void ButtonCount_Click(object sender, EventArgs e)
{
	if (TextBoxSearch.Text != "")
	{
		string result = String.Empty;
		string phrase = TextBoxSearch.Text;
		phrase = phrase.Replace(" ","");
		phrase = phrase.ToUpper();
		char[] c = phrase.ToCharArray();
		Array.Sort(c);

		int index = 0;
		char[] co = new char[c.Length];
		int[] oc = new int[c.Length];

		for (int n = 0; n <c.Length; n++)
		{
			char currentChar = c[n];
			
			if ( IsInArray(co, currentChar) )
			{
				// Update value occurrence of character
				UpdateOccurrence(co, oc, currentChar);
			}
			else
			{
				// Add a new value in the array
				co[index] = currentChar;
				oc[index] = 1;
				index++;
			}
		}

		for (int n = 0; n < co.Length; n++)
		{
			if (oc[n]!=0)
			result += co[n] + " = "+oc[n] + "<br />";
		}

		LabelMessage.Text = result;
		TextBoxSearch.Focus();
	}
}

/// <summary>
/// Update value occurrence of character
/// </summary>
/// <param name="co"></param>
/// <param name="oc"></param>
/// <param name="currentChar"></param>
private void UpdateOccurrence(char[] co, int[] oc, char currentChar)
{
	for (int n = 0; n < co.Length; n++)
	{
		if (currentChar == co[n])
		{
			oc[n] = oc[n] + 1;
		}
	}
}

/// <summary>
/// Check whether the character is in the matrix
/// </summary>
/// <param name="co"></param>
/// <param name="currentChar"></param>
/// <returns></returns>
private bool IsInArray(char[] co, char currentChar)
{
	bool isInArray = false;
	for (int n = 0; n < co.Length; n++)
	{
		if (currentChar == co[n])
			isInArray = true;
	}
	return isInArray;
}

Result of this example: