Here in this C# example, we will show how to add text in new line of Multiline text box. The text will be inserted in new line when user clicks on a button. For a demo purpose, we are taking a DateTimePicker (dateTimePicker1) control, a Button(btnAdd) control and a Multiline TextBox (txtMulti) as shown below.
When user clicks on ADD button, the text in dateTimePicker1 will be inserted into txtMulti. When user again clicks on ADD button after picking another date or with same date, the new date will be inserted into txtMulti.
To achieve this, the C# code to written in click event of ADD button will be like as given below.
private void btnAdd_Click(object sender, EventArgs e)
{
txtMulti.Text += dateTimePicker1.Text + "\r\n";
}