Let us learn how to create a Windows.Forms application for addition and subtraction.
Step 1
Create a new Windows.Forms project.

Add a form into the project.

Add panel and buttons for addition and subtraction.


Step 2

Create user controls for addition.


Step 3

Create an instance of user control in its cs file.
  1. private static Addition _instance;
  2. public static Addition instance {
  3. get {
  4. if (_instance == null) _instance = new Addition();
  5. return _instance;
  6. }
  7. }
Step 4

Call that instance in your form on button click.
  1. private void Add_Click(object sender, EventArgs e) {
  2. panel1.Visible = true;
  3. panel1.Controls.Add(Addition.instance);
  4. Addition.instance.Dock = DockStyle.Fill;
  5. Addition.instance.BringToFront();
  6. }
Step 5

Similarly, do it for subtraction

Now, rebuild your project.
Hence your Windows Form is ready with addition and subtraction user controls.