Form1.cs
namespace WindowsFormsApplication6{public partial class Form1 : Form{public Form1(){InitializeComponent();}int i = 0;private void timer1_Tick(object sender, EventArgs e){i++;txtTime.Text = i.ToString();}private void btnStar_Click(object sender, EventArgs e){timer1.Enabled = true;}private void btnStop_Click(object sender, EventArgs e){timer1.Enabled = false;}private void button1_Click(object sender, EventArgs e){i = 0;txtTime.Text = i.ToString();}}}