Как использовать низкоуровневый winapi для автоматизации приложения

Build a console application that automates a Windows based application which adds , subtracts, multiplies and divides two integers.The automation should be able to launch the application, enter two integers and select an operation and click equals button

private void btnTotal_Click(object sender,EventArgs e)
        {
            try
            {
                double firstnum= Convert.ToDouble(txtFirstNumber.Text);
				double secondnum=Convert.ToDoubletxtSeconNumber.Text);
				char operator;
                switch (operator)
                {
                    case "+":
                        {                     
							lblResult.visible=true;
							lblResult.text="Result is: " + (firstnum+secondnum).ToString();
                            break;
                        }
                    case "-":
                        {
                            lblResult.visible=true;
							lblResult.text="Result is: " + (firstnum-secondnum).ToString();
                            break;
                        }
                    case "*":
                        {
							lblResult.visible=true;
							lblResult.text="Result is: " + (firstnum*secondnum).ToString();
                            break;
                        }
                    case "/":
                        {
							if (secondnum != 0) 
							{ 
								lblResult.visible=true;
								lblResult.text="Result is: " + (firstnum*secondnum).ToString(); 
							} 
							else 
							{ 
								MessageBox.Show("Can't divide by zero"); 
							} 
							break;
                        }
					default:
                        {
                            MessageBox.Show("Invalid Input"); 
                            break;
                        }
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);  
            }
        }