vb.net - Is this program efficient -

i've put small calculator application works quite well, despite being novice vb.net know program isn't efficient should be. idea upon inputting numbers textbox , pressing mathematical operator, textbox reset , continue equation, storing past values entered.

    dim input1 double dim numfunction double 'numerical functions (null = 0, add = 1, subtract = 2, divide = 3, multiply = 4) private sub btnadd_click(sender object, e routedeventargs) handles btnadd.click     if txtnum.text = ""         msgbox("please enter number")     else         numfunction = 1         input1 = input1 + txtnum.text         txtnum.text = ""     end if end sub  private sub btnequal_click(sender object, e routedeventargs) handles btnequal.click     if txtnum.text = ""         msgbox("please enter final number")     end if      if numfunction = 1         txtnum.text = txtnum.text + input1         input1 = 0     end if end sub 

could point me in right direction should replace add or remove make programs more efficient in future? keep in mind btnadd_click event 1 of 4 (add, sub, divide, multiply) , because of btnequal_click have few if statements, checking function user has put in, , if there in txtnum @ all.

thanks in advance, i'm not asking complete code, i'd love see options have make more efficient programs in future.

with little initial effort simplify task using power of object oriented programming:

public class form1     ' hold reference operations in list of operations     private _operations new list(of operation)      ' operation choosen     private property _currentoperation operation      ' 2 numbers want perform operations on     private _number1 double = 0     private _number2 double = 0      public sub new()         initializecomponent()         setupoperations()         textbox1.text = 0     end sub      public sub changeoperation(operation operation)         _number1 = _currentoperation.functiondelegate.invoke(_number1, _number2)         textbox1.text = _number1         _currentoperation = operation     end sub      private sub setupoperations()         _operations.add(new operation(me, btnadd, function(x, y)                                                       return x + y                                                   end function))         ' heres crux ... use anonymous method define functions hook them form (me) , related button         ' @ once         ' similar other operations (subtract / multiply / divide / pow, , on)           dim equalsoperation new operation(me, btnequal, function(x, y)                                                                return y                                                            end function)         _operations.add(equalsoperation)         _currentoperation = equalsoperation     end sub      ' example used 1 textbox , lable indicating wheter number entered valid double     private sub textbox1_textchanged(sender object, e eventargs) handles textbox1.textchanged         dim result double         if double.tryparse(textbox1.text, result)             _number2 = result             lblvalid.text = "valid" ' tell user number entered valid or not         else             lblvalid.text = "invalid"         end if      end sub      ''' <summary>     ''' operation hooks button click , can execute operation     ''' </summary>     public class operation         private _owningform form1         public property functiondelegate func(of double, double, double) ' use delegate func returns double 2 double parameters          public sub new(owningform form1, boundbutton button, functiondelegate func(of double, double, double))             me.functiondelegate = functiondelegate             me._owningform = owningform             addhandler boundbutton.click, addressof boundbutton_click ' make operation hook on click event         end sub          private sub boundbutton_click()             _owningform.changeoperation(me)         end sub      end class  end class 

hope not confusing you, intended show bigger world simple routines , tons of eventhandlers