6/14/2010. VBA program units: Subroutines and Functions. Functions: Examples: Examples:

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1 VBA program units: Subroutines and Functions Subs: a chunk of VBA code that can be executed by running it from Excel, from the VBE, or by being called by another VBA subprogram can be created with the macro recorder or typed in from scratch may have zero-to-several arguments that provide for values to be input to or output from the Sub Sub name (optional arguments) Functions: a VBA subprogram that can be executed by using its name in a VBA expression or an Excel formula functions can return values functions cannot be recorded, but must be typed into the VBE functions may have zero-to-several input arguments Function name (optional arguments) End Function End Sub 1 2 Examples: Examples: Function Twice(mynumber) Twice = 2*mynumber End Function Function Icy(temp) If (temp <= 32) Then MsgBox ("Yes") Icy = temp End Function Sub hello() MsgBox ("Hello") too End Sub MsgBox Hello would work here 3 4 1

2 Declaring variables When you write VBA code, it is possible to get away without declaring the data types of variables that you use. But, this is bad programming practice, so it is best to declare the types of all variables used in VBA: Dim <variable-name> As <type> This requirement is enforced by putting the Option Explicit statement at the top of every VBA module you develop. Making VBA work Save As Macro-Enabled workbook (.xlsm) Make sure Options -> Trust Settings is allowing macros Make a new directory for each VBA/Excel workbook (clarity) Functions: test by calling in Excel worksheet (or from Sub) Allowed to return values Multiple arguments possible Subs: test by running with F8 in VBE Allowed to change cells Multiple arguments possible Check settings by loading Kick Calculator; should run! 5 6 Enforcing variable declaration put Option Explicit statement at the top of every module or set VBE s Tools and VBE will do it for you! Options Require Variable Declaration Object-oriented programming Objects : entities that have attributes ( properties ) that can be manipulated These are generally organized in hierarchies: The object that corresponds to cell A1 Selection Excel Word Microsoft Office 7 Application Objects in red 8 2

3 Object Collections Workbooks all currently-open workbook objects Worksheets all sheets contained in a particular workbook Charts all charts contained in a particular workbook Object-oriented Programming & Variable Scope Referring to objects in a collection Worksheets( Main ) Charts( XY ) Workbook Worksheet Chart Z Y Y X Complete object references Application.Workbooks( Project6 ).Worksheets( Main ).Range( B16 ) Can be simplified when unambiguous Workbooks( Project6 ).Worksheets( Main ).Range( B16 ) X Worksheets( Main ).Range( B16 ) Range( B16 ) 9 10 The SCOPE of a variable How far is the reach of the variable, or from where can the variable be seen? 1) only within a single procedure (Sub or Function) such a variable is generally called a local variable variable is declared using a Dim statement within the procedure 2) only within the current module a module variable declared using a Dim statement before the first Sub or Function in the module 3) everywhere, in all procedures, in all modules open declared using a Public statement at the module level 11 Module 1 Module 2 Dim k As Integer Public R As Single One Dolt Two Howdy Current Workbook/ VBA project 12 3

4 Where can k be referenced? Where can R be referenced? a) Everywhere in Module 1 a) Only Module 1 b) Everywhere in Module 2 b) Only Module 2 c) Anywhere not in Function Dolt c) Only Function Dolt d) Only in Sub howdy d) Only Sub howdy e) Everywhere 13 e) Everywhere 14 Where can y be referenced? Where can j be referenced? a) Only Module 1 a) Only Module 1 b) Function Two and Function Dolt b) Only Module 2 c) Only Function Two c) Only Sub Howdy d) Only Sub Howdy d) Only Function Two e) Everywhere 15 e) Everywhere 16 4

5 Static & Constant Static is used, instead of Dim, when you want the variable to retain its value after the procedure is finished i.e., if you want the variable to have the same value the next time the procedure is run. Static y as Single Symbolic constants can be used to store values with names, where the values should never change. Use the Const keyword for this: Const Rgas As Single = How to invoke Excel spreadsheet functions from VBA: Application.WorksheetFunction.function-name (arguments) Example: creating a function RangeArray uses Min and Max functions in Excel, not available in VBA

6 UserForms UserForms Insert a UserForm in the Visual Basic Editor (VBE) 1) Design it 2) Set up code that processes what the user types into the boxes & clicks on the radio buttons 3) Hook that code to the Compute Re button 4) Set up code that quits & hook it to the Quit button 5) Set up a way to bring up the form 21 Toolbox contains stuff to put on form New & empty form 22 Properties Setting up the name and caption: A user form is a variable and needs a name (like any variable). The Properties window (in the bottom left corner of the VBE) lists properties of the selected object here, the userform. The Name is how you will refer to the form. The Caption is a property of the form what the user sees in the top of the form: Use it to set those properties

7 Add title and field for density Add textbox for value Properties window now refers to the label object Change caption: It s essential to name the textbox since that value will be taken from the user and used in the program. You don t need to change the Name since we re not going to be modifying the label in our program. The Caption is what s displayed on the User Form Add a frame to contain the units choices: Add an option button in the frame for one units choice Frames used to group similar objects. Exclusive OR Must be large enough to include all of the choices you want to provide. Feel free to remove the caption for aesthetic reasons (just remove the text in here) 27 stretch button so caption shows: change title & caption: Again, option buttons MUST be named as that name will be used in your code. 28 7

8 Change default button value to true: Add similar entries for pipe diameter, velocity and viscosity: add button for alternate units with caption and default false: Easiest way: just copy each row and change the names and captions in the corresponding Properties window Add a command button to compute the answer: Change command button name, caption & font: 31 The name of the command button is the name of the VBA subroutine that performs the calculation 32 8

9 Add a Quit button with similar formatting Hooking things up The UserForm is now complete, but two important features are missing: The name of that button is also used in your program. 1) there is no way for the UserForm to appear for use 2) when the Compute and Quit buttons are clicked, nothing will happen because there is no VBA code behind them Hooking VBA code to the Compute Re button Filling in that code: Double-click the Compute Re button. This will cause the following Sub wrapper to pop up in a code module: In here, we must add code to carry out the necessary calculations and display the Reynolds Number result convert units, as required compute the Reynolds Number display the result

10 This variable is the name you created for your textbox What is the variable that VBA uses to return whatever the user types here? Do NOT use the textbox name on the LHS of your calculation it will not work!! This is a variable you create and use in your calculation. 37 a) Diam b) PipeDiameter c) Pipe Diameter 38 What variable does this Sub use in its calculations for this? What is the variable that VBA uses to return whatever the user types here? a) Diam b) PipeDiameter c) Pipe Diameter 39 a) mu b) viscosity c) fluid viscosity 40 10

11 How to run and remove user forms insert a new module and add this Sub to start the UserForm double-click the Quit button and add the code to remove ( unload ) the UserForm run the StartReynoldsNumber macro and enter values with units selected UserForms UserForms can be loaded automatically when the workbook is opened. (This is called an event handler. ) And they can also be unloaded automatically when the workbook is closed. 1. Go to VBE and double click on thisworkbook item in Project Explorer. (If Project Explorer doesn t show up, use view) 2. Change left field at top from General to Workbook. 3. Type in ReynoldsNumber.Show (this is not on any exam; it s just a useful FYI) Things to Remember!!! Create your own variables to carry out calculations, NOT the variables in the user form Make sure the variables from the user form that you assign to your created variables are the same names as in your user form These variables are those used from your text boxes and your option buttons, NOT your labels You should not have the same name for your text box as for your label 43 This variable is the name you created for your option button FormatNumber number of digits after the decimal point. Does not round

12 If you get a Reynolds number of and the program says MsgBox(FormatNumber(Re,1)), what will the message box say? a) 2134 b) 2135 c) d) e) MsgBox Function MsgBox( prompt,buttons, title,helpfile,context) optional MsgBox Function MsgBox( prompt,buttons, title,helpfile,context) optional MsgBox Function Button codes vbokonly vbokcancel vbabortretryignore vbyesnocancel vbyesno vbretrycancel vbcritical vbquestion vbexclamation vbinformation vbdefaultbutton1 vbdefaultbutton2 vbdefaultbutton3 vbdefaultbutton4 vbsystemmodal MsgBox result is button clicked by user Putting line breaks into the message displayed: