Textbox trong lập trình C# Winform

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 TextboxGUI
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            
        }

        private void txbValue_TextChanged(object sender, EventArgs e)
        {
            int num = 0;

            if (Int32.TryParse(txbValue.Text, out num))
                lbValue.Text = (num * num).ToString();
            else
                lbValue.Text = "Vui lòng nhập số!";
        }
    }
}
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namespace TextboxGUI
{
    partial class Form1
    {
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.textBox2 = new System.Windows.Forms.TextBox();
            this.lbValue = new System.Windows.Forms.Label();
            this.txbValue = new System.Windows.Forms.TextBox();
            this.button1 = new System.Windows.Forms.Button();
            this.SuspendLayout();
            // 
            // textBox1
            // 
            this.textBox1.Location = new System.Drawing.Point(35, 39);
            this.textBox1.Multiline = true;
            this.textBox1.Name = "textBox1";
            this.textBox1.ScrollBars = System.Windows.Forms.ScrollBars.Both;
            this.textBox1.Size = new System.Drawing.Size(100, 130);
            this.textBox1.TabIndex = 0;
            // 
            // textBox2
            // 
            this.textBox2.BorderStyle = System.Windows.Forms.BorderStyle.None;
            this.textBox2.Enabled = false;
            this.textBox2.Location = new System.Drawing.Point(161, 39);
            this.textBox2.Name = "textBox2";
            this.textBox2.PasswordChar = '9';
            this.textBox2.RightToLeft = System.Windows.Forms.RightToLeft.No;
            this.textBox2.Size = new System.Drawing.Size(100, 13);
            this.textBox2.TabIndex = 1;
            this.textBox2.Text = "howkteam.com";
            // 
            // lbValue
            // 
            this.lbValue.AutoSize = true;
            this.lbValue.Location = new System.Drawing.Point(32, 220);
            this.lbValue.Name = "lbValue";
            this.lbValue.Size = new System.Drawing.Size(35, 13);
            this.lbValue.TabIndex = 2;
            this.lbValue.Text = "label1";
            // 
            // txbValue
            // 
            this.txbValue.Location = new System.Drawing.Point(35, 186);
            this.txbValue.Name = "txbValue";
            this.txbValue.Size = new System.Drawing.Size(100, 20);
            this.txbValue.TabIndex = 0;
            this.txbValue.TextChanged += new System.EventHandler(this.txbValue_TextChanged);
            // 
            // button1
            // 
            this.button1.Location = new System.Drawing.Point(141, 184);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(75, 23);
            this.button1.TabIndex = 4;
            this.button1.Text = "button1";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.button1_Click);
            // 
            // Form1
            // 
            this.AcceptButton = this.button1;
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(284, 261);
            this.Controls.Add(this.button1);
            this.Controls.Add(this.txbValue);
            this.Controls.Add(this.lbValue);
            this.Controls.Add(this.textBox2);
            this.Controls.Add(this.textBox1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.TextBox textBox1;
        private System.Windows.Forms.TextBox textBox2;
        private System.Windows.Forms.Label lbValue;
        private System.Windows.Forms.TextBox txbValue;
        private System.Windows.Forms.Button button1;
    }
}

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