string theDate = dateTimePicker1.Value.ToShortDateString();

string theDate = dateTimePicker1.Value.ToString("yyyy-MM-dd");

string shortDate = dateTimePicker1.Value.ToShortDateString();

public MyClass()
{
    // Create a new DateTimePicker
    DateTimePicker dateTimePicker1 = new DateTimePicker();
    Controls.AddRange(new Control[] {dateTimePicker1});
    MessageBox.Show(dateTimePicker1.Value.ToString());

    dateTimePicker1.Value = DateTime.Now.AddDays(1);
    MessageBox.Show(dateTimePicker1.Value.ToString());
 }