Liên kết: Hình Chữ Nhật + Hình Hộp + Form1

// Hình Chữ Nhật

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WindowsFormsApp3
{
    class HCN
    {
        public int cd;
        public int cr;
        public HCN(int cd,int cr)
        {
            this.cd = cd;
            this.cr = cr;
        }
        public int tinhDT()
        {
            return cd * cr;
        }
        public int tinhCV()
        {
            return (cd + cr) * 2;
        }
        public String xuatTT()
        {
            return "dt: " + tinhDT() + " cv: " + tinhCV();
             
        }
    }
}

// Hình Hộp

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WindowsFormsApp3
{
    class HH : HCN
    {
        public int cc;
        public HH(int cd,int cr,int cc):base(cd,cr)
        {
            this.cc = cc;
        }
        public int tinhTT()
        {
            return tinhDT() * cc;
        }
        public String xuatTT()
        {
            return base.xuatTT() + " tt: " + tinhTT();
        }
    }
}




// Form1
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 WindowsFormsApp3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void checkBox1_CheckedChanged(object sender, EventArgs e)
        {
            if(checkBox1.Checked==true)
            {
                label3.Enabled = true;
                textBox3.Enabled = true;
            }
            else
            {
                label3.Enabled = false;
                textBox3.Enabled = false;
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            int cd=int.Parse(textBox1.Text);
            int cr = int.Parse(textBox2.Text);
            if(checkBox1.Checked==true)//hinh hop
            {
                int cc = int.Parse(textBox3.Text);
                HH a = new HH(cd, cr, cc);
                label4.Text= a.xuatTT();
            }
            else
            {
                HCN a = new HCN(cd, cr);
                label4.Text = a.xuatTT();
            }
        }
    }
}