change forecolor for words that contains X in rich textbox

  private void richTextBox1_KeyUp(object sender, KeyEventArgs e)
  {
  string word;
  FontStyle fs;
  if (start > -1 && end > start && e.KeyData == Keys.Space)
  {
  word = richTextBox1.Text.Substring(start+1, end - (start+1));
  if (word.ToUpper().Contains("X"))
  {
  fs = FontStyle.Bold;
  richTextBox1.Select(start, end);
  richTextBox1.SelectionColor = Color.Red;
  richTextBox1.SelectionFont = new Font(richTextBox1.SelectionFont, fs);
  richTextBox1.Select(end + 1, 0);

  }
  start = end;
  fs = FontStyle.Regular;
  richTextBox1.SelectionColor = Color.Black;
  richTextBox1.SelectionFont = new Font(richTextBox1.SelectionFont, fs);

  }
  }

  private void richText1_KeyPress(object sender, KeyPressEventArgs e)
  {
  if (e.KeyChar == ' ')
  {
  if (start == -1)
  start = richTextBox1.TextLength;
  if (start >= 0 && richTextBox1.TextLength > start)
  end = richTextBox1.TextLength;

  }
  }

This is just an example of how you can do it but you have a lot of work to do to get it to work for ALL conditions, for example you may need to track every single word position that contains an X in it, this could be done with an array of Points eg Point p = new Point(x, y);



x being the start of the word, y being the end but then you would need to know about paragraphs, line number etc .....