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1 This content has been downloaded from IOPscience. Please scroll down to see the full text. Download details: IP Address: This content was downloaded on 31/01/2018 at 06:24 Please note that terms and conditions apply. You may also be interested in: Modelling Physics with Microsoft Excel : B Random V Liengme events Interactive Learning Media for Lenses and Their Applications Using Macro Visual Basic in Microsoft PowerPoint Sari Sami Novita, Siti Nurul Khotimah and Wahyu Hidayat Preparing content-rich learning environments with VPython and Excel, controlled byvisual Basic for Applications Chandra Prayaga An Excel texttrademark model of a radioactive series D G H Andrews The Euler s Graphical User Interface Spreadsheet Calculator for Solving Ordinary Differential Equations by Visual Basic for Application Programming Kim Gaik Tay, Tau Han Cheong, Ming Foong Lee et al. Investigating complexity using Excel and Visual Basic K P Zetie An automated HAXPES measurement system with user-friendly GUI for R kev at BL46XU in SPring-8 H Oji, T Matsumoto, Y-T Cui et al. Research on AutoCAD secondary development and function expansion based on VBA technology Runmei Zhang and Yehuan Gu

2 IOP Concise Physics Excel VBA for Physicists A Primer Bernard V Liengme Chapter 1 Introduction Visual Basic for Applications (VBA) is a programming language that has been built into Microsoft Office since Office It has its roots in Visual Basic (VB), so when you perform an internet search on a VBA topic do not be surprised by references to VB. In this chapter we will make a few simple changes to our Excel environment to allow us to code and run macros. Then we will see how to code some examples of simple macros (procedures), i.e. functions and subroutines. We close with a brief look at recording a subroutine. 1.1 Preparation There is little to do in preparation. We start by adding the Developer tab to the Excel ribbon. Right click on the Home tab and select Customize Ribbon. This opens the dialog box as shown in figure 1.1, click the box to the left of Developer to add a check mark (if it is not already there), and then click the OK button in the lower right-hand corner of the dialog. As can be seen from the title in this dialog, one can also customize the ribbon by using the command File Options Customize Ribbon. The ribbon now has the Developer tab present, as shown in figure 1.2. We can now check the macro security setting. Open the Developer tab and click on Macro Security to open the dialog shown in figure 1.3. Make sure that the setting is Disable all macros with notification (this is the default setting and should not be changed without good reason.) Beginning with Office 2007, Microsoft required that workbooks containing macros be saved with the extension XLSM; we refer to such workbooks as macro-enabled. This is a security feature since a rogue macro can harm a computer. When you open a macro-enabled workbook you will see a warning as shown in figure 1.4; click on Enable Content if you trust the workbook not to have rogue macros. If you are working with Excel 2003, your workbooks will have the extension XLS even when they contain macros. To learn more about macro security, visit Office-files-12B036FD-D140-4E74-B45E-16FED1A7E5C6. doi: / ch1 1-1 ª Morgan & Claypool Publishers 2016

3 Figure 1.1. Customizing the Quick Access Toolbar to add the Developer tab. Figure 1.2. The ribbon with the Developer tab added. You may not see this warning every time; Excel seems to remember if a specific macro-enabled file has been opened in the same user session. At other times the warning comes with a more ominous message (figure 1.5). It seems odd that this message occurs when the file sits on the author s hard drive. In subsequent chapters all the reader needs to do is open one of the workbooks (Topic2.xlsm to Topic8.xlsm) which are available for download see the preface. In this chapter the reader needs to learn how to open the VB Editor (VBE), add a module, and save a macro-enabled file. It is best that the reader starts with a new file. However, to cut down on the work, the companion site has the file Topic1BVL.xlsm, and this chapter gives instructions on copying from that workbook to the reader s new workbook. 1-2

4 Figure 1.3. Setting the macro security. Figure 1.4. Example of a macro warning. Figure 1.5. Another macro warning format. 1.2 Demonstrating a simple function Within the Excel environment there are three types of function: the worksheet function (examples being SUM, AVERAGE, ACOS); VB functions (Lcase, Len, Round); 1-3

5 and functions that are coded by a user. Functions of the last type are often referred to as user-defined functions (UDFs). Later we will see that all VB functions may be used within a UDF, but there is a restriction on which worksheet function may be used. In general, if there is an equivalent VB function then the worksheet function may not be used. Example. A physics student needs to compute the kinetic energy given the mass and velocity of the object. Figure 1.6 shows a sample worksheet. In column C he uses a worksheet formula to compute the kinetic energy, while column D shows how a UDF may be used. The reader should set up a worksheet like this but leave D2:D5 empty for now. In B7 we have the formula = FORMULATEXT(C2), which displays the referenced cell s formula. Open the Developer tab, click on Visual Basic (the left most icon) to open the VBE. Figure 1.7 shows the VBE window, but since you have just opened it the working space (the module area, the panel at top right) will be grey. Click on the Insert command and select Module. Now type this code into the module: Function KE(mass, Vel) KE = (1 / 2) * mass * Vel ^ 2 End Function You may now return to the worksheet by clicking the green Excel icon on the far left of the VBE toolbars, or by clicking the worksheet if it is visible behind the VBE. In D2 type =KE(A2, B2), press Enter to complete the formula, and drag the formula down to row 5. Suppose you made a mistake in the code and had entered KE = (1/2) *mass*vel+2. You can return to the VBE (try the shortcut ALT+F11) and make the correction. How disappointed will you be when on returning to the worksheet you find the results in columns C and D still do not agree? MORAL. Whenever a change is made to a UDF it will not affect the worksheet until the worksheet is recalculated. Do this by pressing F9, or selecting a cell with the UDF (D2 for example) and double clicking it. Figure 1.6. Example of using a UDF. 1-4

6 If you have a syntax error in a macro, Excel will throw up a warning. Click the Debug button and the offending line will be highlighted. After making a correction, click the square blue reset button it is right under Run in the menu bar of the VBE as shown in figure 1.7. When there is a VBA error you cannot do anything with the worksheet until the error is removed. 1.3 Saving a macro-enabled workbook Now we will save our work. From the Excel workspace either click the Save icon in the Quick Access Toolbar (will Microsoft think of a new icon when we have all forgotten about floppy discs?) or use the command File Save. In the normal way, give the file a name such as Topic1 but there is an extra step. Under the name box you will see a box Excel Workbook (.xlsx) with a drop down arrow at the right. Click the arrow and select the second option, Excel Macro-Enabled Workbook (.xlsm), see figure 1.8. If you fail to do this Excel will detect the presence of a macro and issue a warning. If you do not heed the warning all your modules will disappear! Figure 1.7. The VBE interface. Figure 1.8. The macro-enabled option in Save. 1-5

7 1.4 Using constants and VB functions Professor X wants to make a worksheet to compute the most probable, the mean, and the root-mean-squared velocity of various gases at a specified temperature. Her worksheet is shown in figure 1.9. Once again we will perform our calculations first with worksheet formulas and then with UDFs. The author likes to confirm that the two methods agree when testing a new UDF. The formulas for the three velocities in C10:E10 are: =SQRT(2*8.3145*Temp/ (B10*10^-3)), =SQRT(8*8.3145*Temp/(PI()*B10*10^-3)), and =SQRT ((3*8.3145*Temp)/(B10*10^-3)). Note that B6 has been given the name Temp. Open your Topic1.xlsm workbook, add a new worksheet and make it similar to the figure. The reader may wish to open Topic1BVL.xlsm, select A1: F29, and copy and paste to his/her Sheet2. Initially this will give #NAME! errors Figure 1.9. Another UDF. 1-6

8 in C18:E21 and C26:E29 because the Topic1.xlsm workbook lacks the referenced UDFs. Open the VBE. Sometimes it is expedient to have more than one module, but that is not the case here. On Module1 add the following code below the code for the kinetic energy function (as we are working in SI units we need the molar mass to be in kilograms, hence the 10 3 factor): Function Vprob(T, M) Const R = SI units Vprob = Sqr(2 * R * T / (M * 10 ^ 3)) End Function In C18 enter the formula =Vprob(Temp, B18). Infigure 1.9 the inset shows that our UDF appears in the tooltip box when we type =v. In the function code we have declared R to be a constant and given it a value. This prevents users from reassigning a value to R later in the code not very likely in a two-statement function but a potential error in longer macros. Within the code Const R = SI units, everything after the single quote is a comment. Since VB functions take precedence over worksheet functions we use its Sqr function rather than the worksheet function SQRT. The code for Vmean is shown below; it is left as an exercise for the reader to code Vrms: Function Vmean(T, M) Const R = SI units Pi = 4 * Atn(1) Vmean = Sqr(8 * R * T / (Pi * M * 10 ^ 3)) End Function We will code the UDF used in C26:E29 shortly. Two things to note: (i) VB has no built in function for π, we could have coded Pi = , but to guard against typing errors we choose the simple formula; (ii) VBA permits a constant to be defined with an expression such as Const TwoPi=2 * , but functions are not permitted in the expression, making Const Pi = 4 * Atn(1) invalid. While researching these formulas for these velocities, the author found several sites that computed them. All agreed when the root-mean-squared velocity was calculated, but there was a wide spread for the others. To test for correctness, use the fact that vmean = ( π ) vprop and vrms = vprop. The following website gave consistent results: User-defined array functions It is possible to write code that returns data to more than one cell think about the worksheet functions LINEST and FREQUENCY. The code below computes Vprob, Vmean, and Vrms all in one function. If you pasted C26:E29 from the author s 1-7

9 workbook, please delete those cells now. Select C26:E26, type =Velocities (Temp,B26) and commit the formula with CTRL+SHIFT+ENTER. Cells C26: E26 will each display {=VelocitiesV(Temp,B26)} where Excel has added the curly braces to denote an array function. We can now drag C26:E26 down to row 29. Function Velocities(T, M) Dim Vel(3) Const R = Pi = 4 * Atn(1) Vel(0) = Sqr(2 * R * T / (M * 10 ^ 3)) Vel(1) = Sqr(8 * R * T / (Pi * M * 10 ^ 3)) Vel(2) = Sqr(3 * R * T / (M * 10 ^ 3)) End Function In the first statement we use the Dim feature to define an array called Vel having three components. We compute values for each component and then pass the values of the Vel array to the function named Velocities. Unless the reader is familiar with languages like C++, the use of Vel(0) might be a bit unsettling. By default, VB uses array indices starting with zero; chapter 2 shows how we can obtain the more familiar first index of Notes on VBA functions Because the marriage of Office Excel and VB was made when both were mature applications, it is not surprising that sometimes there is a clash between them. The reader should be aware that there are some differences between worksheet and VB functions with the same name. 1. While the worksheet function =LOG(3) returns the logarithm of 3 to base 10, the VB expression x = Log(3) results in the logarithm to base e. To obtain a base 10 result one codes x = Log(3)/log(10). 2. When the digit to be rounded is 5, the VB Round function rounds to make the result even; so Round(3.5,0) and Round(4.5,0) each give 4 as the result, and Round( 3.5,0) and Round( 4.5,0) each give 4. Contrast this with the Excel results, which would be 4 and 5 for positive values and 4 and 5 for negative values, since Excel rounds up when x > 0 and down when x < 0 when the digit to be rounded is 5. The VB behavior is sometimes called bankers rounding, but there is little evidence that bankers use it. 3. Excel has the MOD function: =MOD(11,10) returns the value 1. VBA has the Mod operator: the expression 11 Mod 10 also returns 1. However, the two do not agree when one (not both) of the arguments is negative, as is shown in table 1.1; the last two columns show alternative ways of performing the calculations. TRUNC and INT are similar in that both return integers. TRUNC removes the fractional part of the number. INT rounds numbers down to the nearest integer based on the value of the fractional part of the number. The results from INT and TRUNC are different only when using negative numbers: 1-8

10 Table 1.1. Comparing Excel s MOD and VBA s Mod. a b MOD Mod a-(b*int(a/b)) a-(b*trunc(a/b)) Figure Example of output from a subroutine. TRUNC( 4.3) returns 4, but INT( 4.3) returns 5, because 5 is the lower number. The table above is taken from ui=en-us&rs=en-us&ad=us. 1.7 A simple subroutine In this section we see a simple subroutine that asks for input from the user and, having made a calculation, places the result on a worksheet. For the demonstration it is convenient to stay with the molecular velocities theme. Using the icon of an X within a circle after the last sheet tab, the reader should insert a new worksheet. Then right click its tab and rename the sheet MolVel. Set up the worksheet to look like figure 1.10, leaving rows 4 and 7 empty. Using the command Insert Illustrations Shapes, place any shape on the worksheet and add text to it. Navigate to the VBE and in the Project panel (top left) select Topic1. From the menu, use Insert Module. It is not essential to put our code in a separate module, but it helps with the demonstration. Enter the code shown below, this may be copied from Module2 in Topic1BVL. xlsm: Sub MolVel() On Error GoTo Hades Worksheets( MolSpeed ).Activate Range( B4:D4 ).ClearContents 1-9

11 Range( B7:D7 ).ClearContents Gas = InputBox(prompt:= Give gas name or formula ) Range( B4 ) = Gas MolMass = InputBox(prompt:= Give molar mass (g/mole) ) Range( C4 ) = MolMass mtemp = InputBox(prompt:= Give temperature in K ) Range( D4 ) = mtemp Range( B7 ) = Vprob(mTemp, MolMass) Range( C7 ) = Vmean(mTemp, MolMass) Range( D7 ) = Vrms(mTemp, MolMass) Hades: End Sub Experienced programmers may be appalled to see a GoTo, but the construct On Error GoTo is very common in VB programming, especially in the form On Error GoTo Resume Next to tell the program to ignore any error it encounters. Here we have made up a name Hades for a line to which the program will go when an errorisdetected.theprogramflow is directed to the very end of the subroutine in this circumstance. Examples of possible errors: (i) there is no worksheet called MolSpeed or (ii) the user fails to enter a meaningful value for one of the numeric variables MolMass and mtemp, 1 causing the various velocity functions to misfire. Note how we can access these velocity functions even though they reside on a different module within the same workbook. Should we wish to prevent such access we could add the word Private at the start of a function header Private Function Whatever(.). Before we proceed we need to return to the worksheet. Right click on the shape and by selecting Assign Macro, indicate that this shape should run the subroutine MolVel when clicked. Next we look at various ways of calling up the subroutine. 1. Within the VBE we could use the Run command (figure 1.11) on the menu (or its shortcut F5), or click the green arrow just below the Debug menu command. In these cases, VBA may present a dialog box listing the macros (i.e. subroutines) in the current VBA Project even when there is only one! Click on the macro of interest and then click the Run button, or just double click the sub you wish to run. If the mouse cursor is inside a subroutine this dialog is often skipped. 2. In the Code group (far left) of the Developer tab click on the item Macros, or on the View tab locate the Macros group (far right), click on the Macros tool, and select View Macros. In either case a dialog will open with a list of macros not just those in the current project but all those in the currently opened workbook. The shortcut ALT+F8 results in the same dialog. 3. Click on the shape on the MolSpeed sheet. Since we have assigned it to the MolVel subroutine this is what will run. 1 A variable must not have a name which is also a keyword, so we used mtemp rather than Temp just in case Temp is a keyword (actually, it is not!). 1-10

12 Figure Some commands in the VBE menu. Figure The InputBox dialog. When we run MolVel, Excel is told to activate the appropriate sheet, otherwise our output could damage another worksheet. Of course, if we always ran the sub by clicking the shape on the MolSpeed worksheet, this statement would be redundant. Next a box pops up (figure 1.12) asking the user to name the gas. This name is then placed in cell B4. In similar ways we obtain the molar mass and temperature in B5 and B6, respectively. These are used by the velocity functions (Vprob, Vmean, and Vrms) and the results of the functions are placed in cells B7:D7. Note that this subroutine that resides in Module2 has access to functions defined in Module1. If we wished otherwise we would add the word Private before Function in the headers. 1.8 Linking an image to a subroutine In figure 1.10 we have a blue rectangle which, when clicked, causes the subroutine MolVel to run. The image can be a shape or picture. After placing it on the worksheet right click it to bring up the dialog shown to the left in figure The user clicks the Assign Macro item bringing up a list of subroutines available in the current Excel session and clicks the appropriate one. 1.9 Recording a macro Excel has a tool for recording the user s keystrokes and generating a subroutine that can be used over and over. This can be useful for formatting and entering textual data. 1-11

13 Figure Linking an image to a subroutine. Figure The Record Macro dialog. It cannot be used to make functions or to have a subroutine place a value in a cell. Many users have found the Recorder useful for learning simple VBA commands, but it must be stressed that the resulting subroutine is seldom very efficient. Let us see an example. Open Sheet2 of the Topic1 workbook. To the left of the status bar just after the word Ready, there is a small box which switches the recorder on and off. The Code group of the Developer tab also has this tool. Start recording and perform the following operations: 1. Fill in the dialog box as shown in figure 1.14 and click the OK button. We will not bother with a shortcut. 1-12

14 2. Hold down the CTRL key and drag the tab of Sheet2 to the left between Sheet2 and MolSpeed. Release the CTRL key. Now we have a new worksheet called Sheet2 (2) and it is the active sheet. 3. Using tools in the font group of the Home group: i. Change the size of the type in A1:E1 and A6:C6. ii. Select A8:E13 and give the range a fill colour and change its font colour. iii. Do the same with A16:E21. iv. Click on F Switch off the recorder. Open the VBE and in the Topic1 project you will find the recorder added Module3 holding the sub DuplicateSheet2. This reads: Sub DuplicateSheet2() DuplicateSheet2 Macro Make a duplicate of Sheet2 and format some ranges Sheets( Sheet2 ).Select Sheets( Sheet2 ).Copy Before:=Sheets(3) Range( A1:E1 ).Select Selection.Font.Size = 14 Selection.Font.Size = 16 Range( A6:C6 ).Select Selection.Font.Size = 14 Selection.Font.Size = 16 Range( A8:E13 ).Select With Selection.Interior.Pattern = xlsolid.patterncolorindex = xlautomatic.themecolor = xlthemecoloraccent3.tintandshade = PatternTintAndShade = 0 End With With Selection.Font.ThemeColor = xlthemecoloraccent2.tintandshade = 0 End With Range( A16:E21 ).Select With Selection.Interior.Pattern = xlsolid.patterncolorindex = xlautomatic.themecolor = xlthemecoloraccent1.tintandshade = PatternTintAndShade = 0 End With 1-13

15 With Selection.Font.ThemeColor = xlthemecoloraccent5.tintandshade = End With Range( F14 ).Select End Sub The reader is encouraged to spot the pieces of code that correspond to the actions performed while recording. Of course, some parameters (such as Font.Size, TintAndShade) will have different values depending on what the user selected Finding a home for macros We have placed our functions and subroutines in modules stored in the current workbook. This is generally the safest choice. Macros housed in other workbooks are accessible when those workbooks are open; one generally avoids this complication. If you have macros that you wish to use in many different workbooks, then the best course is to store them in the Personal.xlsb workbook. This workbook can be made by starting the recorder, specifying Personal as the stage place (the third box in figure 1.14), and recoding a one-line sub. Then go to the VBE, open the Personal project, and delete the module with the dummy subroutine. The Personal.xlsb workbook is stored in your Xlstart folder and opens every time Excel is started, and it is normally hidden in Excel but visible in the VBE. The following links provide further information (do not be concerned if they mention older versions of Excel or Windows): Workbook-AA439B90-F F0-6E4C3F5EE566?ui=en-US&rs=en- US&ad=US Another place for macros is an Add-in workbook; we explore this topic in chapter Typographical matters The indentation shown in our example is not mandatory but is highly recommended as it makes reading the code a lot easier. For example, when the statements between For and Next are indented it is immediately obvious what code is repeated. A long statement may be split into several rows using the underscore character. For example: Range( A2 ) = Range( F2 ).Value + Range( C2 ).Value may be coded as Range( A2 ) = Range( F2 ).Value _ + Range( C2 ).Value 1-14

16 It is important to note that the underscore is placed just after a space in the long code. This cannot be a space within a literal. The correct way to split a literal is demonstrated by Range( A10 ) = Now is the time for all good folks to _ & come to the aid of the party 1-15