F001. Hello

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 F001_Hello
{
    public partial class Form1 : Form
    {
        bool flag = false; //변수
        public Form1() //생성자 함수 
        {
            InitializeComponent(); //자동
        }

        private void Form1_Load(object sender, EventArgs e) //이벤트 함수
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {

            if (flag == false)
            {
                label1.Text = "Hello World!";
                flag = true;
            }
            else
            {
                label1.Text = " ";
                flag = false;
            }
        }
    }
}