VBA Basics

8/12/2019 VBA Basics

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Dr. Antonio A. Trani

VBA Principles

CEE3804: Computer

Applications for

Civil and

Environmental

Engineers


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Objectives

! Develop a simple set of programs in VBA! Learn to execute a macro from within a

worksheet

! Introduction to loop structures

CEE 3804


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Before You Program

! Develop a strategy to solve the problem! Develop pseudo-code! Develop a flowchart (helps guide your thought process)

! NOTE: most engineers do not to like to develop flowcharts! This creates problems when someone else looks at your program! Most programs do not work the first time, so a flowchart of pseudo-

code can help you understand bad logic

Start

Output

c

Inputb

c = a + b

Inputa

End

Start here:

Flowchart Then code


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Flowchart Symbols

! Review them in Chapras book (page 115)Symbol Name Function

Terminal Represents the

beginning of end of a

programFlow lines Represent the flow of

logic

Process Calculation of data

manipulation

Input/Output Represents input and

output of data andinformation

Decision Represents a

comparison or a

condition with more

than one path

Start

c = a + b

Input

b

If (a>b) True

False


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Flowchart Symbols (cont.)

Symbol Name Function

Count-controlled

loop

Indicates the number

of times a loop is

excecutedJunction or

connector

Represents a

confluence of flow

lines

Off-page connector Break or continuation

to another page

Stored data Represents datastorage in a database


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A Simple VBA Program

! Lets develop a simple program in VBA tocalculate the sum of two numbers of a

worksheet

! The program should retrieve two numbers fromsheet1in a standard Excel worksheet

! The program should add the two numbers andreturn the result to the worksheet

!Place a run

button in the worksheet tofacilitate future execution of the subroutine


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Program Flowchart

! Here is a basic flowchart to build this programStart

Outputc

Inputb

c = a + b

Inputa

End

Start

Outputc

Input

b

c = a + b

Input

a

End

Version 1

Version 2


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Excel Worksheet (final program)

CEE 3804 : A.A. Trani


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VBA or Macros in Old Excel Versions(including Mac 2011)

! Go to: Tools/Macro! Then select VBA


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VBA or Macros in Excel WIN 2013

! Go to : Developer Tab! Then Click Visual Basic



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VBA Code

Name of subroutine

Go to sheet1Select the value of cell B7

and assign it to variable a

Select the value of cell B8

and assign it to variable

bCalculate the value of c

Select cell B8 and assign it

to variable c



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Adding the RunButton

! Adding the runbutton requires that you inserta control button and then assign a macro to

subroutine adder



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Assigning the Behavior to theRunButton

! Assign the macro adderfrom the list ofavailable macros to button Run

! Right-click on the button to assign a behavior


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Test Your Program

! Test the program to make sure it works

! Try variations of the program as well


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Subroutine Adder1 with Input Box

! This variation of the program creates an inputbox for the first number

String variable a

is read using an

input box

Returns the

number

contained in the

string a


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Excel Help for VAL Function


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Executing the New Program



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A Simple Program with a Loop

! Loops are natural ways to executecomputations that require multiple iterations

! Loops can be conditioned or controlled by acounter

! Conditional loops - when some condition isused to exit the loop

!Counter controlled loops - when the number ofpasses in the loop is known


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First Program with a Loop


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The VBA Code Behind

Loop code



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A Loop with Concatenation Control

! The program in worksheet: loopConcatenate.xlsoffers a sample of a loop computation and the

use of concatenation control to estimate

pavement thicknesses

! The pavement thickness function created inprevious classes in calledby the VBA code



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Worksheet Interface

Cell B8 controls the

number of times theloop is executed



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The Code Behind the Worksheet



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Code (cont.)

Calculates pavement thickness

Concatenation



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Try Other Refinements

! Currently the loop counter just overwrites thevalues of pavement thickness without erasing

previous computation

! Try adding a line or two of code to erase theprevious table of computations while executingthe code

Use a statement such as : Range(A1:C5).clear This clears the range between cells A1 and C5 You can always clear a large range of cells so that

your program will always work correctly



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Simple Control Structure

! If-Then-Else is a powerful, yet simple controlstructure that could be used to make

branching decisions in a program

If (condition) then! Code 1 is executed

Elseif (condition 2) then! Code 2 is executed

Elseif (condition 3) then! Code 3 is executed

End if!You can add as many else-if-then statements as

needed in your program logic

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Modification of Pavement Analysis Program(Loop with Concatenation)

! Suppose we would like to modify the previouslycreated program to replace the value of

California Bearing Ratio (CBR) for the type of

soil used in construction

! Suppose we have a simple table with typicalvalues of CBR as follows:

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Material Value of CBR (dim)

Crush stone 100

Sandy soil 25

Silty soil 13

Clay soil 7

Organic soil 4



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! Recall the original spreadsheet

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Material Value of CBR (dim)

Crush stone 100Sandy soil 25

Silty soil 13

Clay soil 7

Organic soil 4



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! Create a list of items to be selected by the user incell B7

! Use the Data Validation in the Data Tab! Create a list in the validation criteria

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! The list of items can be enumerated in anothersection of the spreadsheet

! In this example I used cells G7:G11 to write thenames of the types of soils to be selected

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! Once the cell is connected with data validation onlythe names of the soils types can be selected in that

cell

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! Complete the VBA code to assign the value of CBRfor a selected soil type entered in cell B7

! Use the if-then-else statement construct

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Retrieves the content

of cell B7

The If-Then-Else block

assigns a value of

cbr to the selected

soil type



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Last Word Exemption Handling

! It is always a good idea to handle anomalous conditionsin your program gracefully

! You should always include an Else statement tohandle bad inputs

!Below we warn the user if the soil could not be matched

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Documents

VBA Basics