Step 1: Click New Project, then select Visual C# on the left, then Windows and then select Windows Forms Application. Name your project "Countdown" and then click OK
Step 2: Design your form as below

Step 3: Add code to handle your form as below
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace Countdown
{
public partial class Form1 : Form
{
System.Timers.Timer t;
int h, m, s;
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
t = new System.Timers.Timer();
t.Interval = 1000;//1s
t.Elapsed += OnTimeEvent;
}
private void OnTimeEvent(object sender, System.Timers.ElapsedEventArgs e)
{
Invoke(new Action(() =>
{
s += 1;
if (s == 60)
{
s = 0;
m += 1;
}
if (m == 60)
{
m = 0;
h += 1;
}
//Update textbox
txtResult.Text = string.Format("{0}:{1}:{2}", h.ToString().PadLeft(2, '0'), m.ToString().PadLeft(2, '0'), s.ToString().PadLeft(2, '0'));
}));
}
private void btnStart_Click(object sender, EventArgs e)
{
t.Start();
}
private void btnStop_Click(object sender, EventArgs e)
{
t.Stop();
}
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
//Stop timer
t.Stop();
Application.DoEvents();
}
}
}
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