Date Calculator using C#

//declaring the variables
int intervaldate; //represents a date interval
DateTime dateresult; //represents the added date of start date and the interval days
string msg; //repesents a message to put into a listbox

private void txtafter_TextChanged(System.Object sender, System.EventArgs e)
{
	try
	{
		//conditioning the after days interval
		if (txtafter.Text.Length > 0) //check the interval days if greater than 0.
		{
			intervaldate = system.convert.toint32(txtafter.text); //assigning a textbox to a varialble
			//formula
			dateresult = dtpstrdate.Value.AddDays(intervaldate).ToString(); //adding the interval days to the start date.
			msg = "After " + intervaldate + " day(s), the date is "; //message to be put in the listbox
			ListBox1.Items.Clear(); //clearing a listbox
			ListBox1.Items.Add(msg + Format(dateresult, "dddd, MMMM dd, yyyy")); //adding a message and formatted date result in the listbox
			txtbefore.Clear(); //clearing the textbox
		}
		else
		{
			ListBox1.Items.Clear(); //clearing a listbox
		}
	}
	catch (Exception ex)
	{
		MessageBox.Show((string) ex.Message);
	}
 
 
}

private void txtbefore_TextChanged(System.Object sender, System.EventArgs e)
{
	try
	{
		//conditioning the before days interval
		if (txtbefore.Text.Length > 0)
		{
			intervaldate = System.Convert.ToInt32(txtbefore.Text);
			//formula
			//syntax...
			//the formula is the same but the twist is
			//i add a negative interval so that it will go back to the previous date.
			dateresult = dtpstrdate.Value.AddDays(- intervaldate).ToString();
			msg = "Before " + intervaldate + " day(s), the date is ";
			ListBox1.Items.Clear();
			ListBox1.Items.Add(msg + Format(dateresult, "dddd, MMMM dd, yyyy"));
			txtafter.Clear();
		}
		else
		{
			ListBox1.Items.Clear();
		}
	}
	catch (Exception ex)
	{
		MessageBox.Show((string) ex.Message);
	}
}