Creating and using DLL (Class library) in C#

A DLL (Dynamic Link library) is a library that contain some functions (code) and data which can be used by more than one program at a same time. Once we have created a DLL file, we can use it in many application. The only thing we have to do is to add the reference/Import the DLL File.

Creating DLL File:-

Step 1: Open Visual Studio -> Click on File->New Project -> Visual C# -> Class library

Step 2:- Change the class name(class1.cs) to calculate.cs

Step 3:- in calculate class write method for addition and subtraction of two integer.

Step 4:- Build the solution (F6). If Build is succeeded than you will see calculation.dll file in bin/debug directory of your project.

We have created our DLL file. Now we are going to use it in another Application.

Using DLL File:-

Step 1:- Open Visual Studio-> Click on File -> New Project ->Visual C# ->Windows Form Application

Step 2:- Design form as in below picture

Step 3:- Add Reference of dll file i.e. calculation.dll that we have created earlier.

Step: 4:- Add namespace (using calculation)

Step 5:-

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

using Calculation;

namespace MiniCalculator

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }

        calculate cal = new calculate();

        //Addition Button click event

        private void button1_Click(object sender, EventArgs e)

        {

            try

            {

                //storing the result in int i

                int i = cal.Add(int.Parse(txtFirstNo.Text), int.Parse(txtSecNo.Text));

                txtResult.Text = i.ToString();

            }

            catch (Exception ex)

            {

                MessageBox.Show(ex.Message);

            }

        }

        //Subtraction button click event

        private void button2_Click(object sender, EventArgs e)

        {

            try

            {

                //storing the result in int i

                int i = cal.Sub(int.Parse(txtFirstNo.Text), int.Parse(txtSecNo.Text));

                txtResult.Text = i.ToString();

            }

            catch (Exception ex)

            {

                MessageBox.Show(ex.Message);

            }

        }

    }

}