how to reduce line number when wordwrap on and off

Question

I developed a notepad application . In that i used Line Numbers and wordwrap and all.
My Problem is when i click wordwrapItem.Click=false it will not reduce the line number in
Label. This is My Code:

private void UpdateNumberLabel  
{  
Point pos = new Point(0, 0);  
int firstIndex = richTextBox1.GetCharIndexFromPosition(pos);  
int firstLine = richTextBox1.GetLineFromCharIndex(firstIndex);  

pos.X = ClientRectangle.Width;  
pos.Y = ClientRectangle.Height;  
int lastIndex = richTextBox1.GetCharIndexFromPosition(pos);  
int lastLine = richTextBox1.GetLineFromCharIndex(lastIndex);  
pos = richTextBox1.GetPositionFromCharIndex(lastIndex);  
UpdateLabel.Text = "";  
int i=0;  
for (i = firstLine; i <= lastLine + 1; i++)  
{  
UpdateLabel.Text += i + 1 + "\n";                      
}  
}