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CSI 1306

PROGRAMMING IN VISUAL BASIC

PART 5

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Part 5

1. Procedures

2. Sub Procedures

3. Function Procedures

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Procedures

A procedure is a block of VB code entered in a

VB module that is executed (run) as a unit

Many procedures can be entered in a singlemodule

Many modules can be added to a single workbook

To add a new module to a workbook, select Module

from the Insert menu

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Procedures

When we subdivide a problem, translating the

solution into Visual Basic code involves

Translating the algorithm for each smaller problem into

a Visual Basic procedure

Developing a main procedure (with actual parameters)

that assembles the other procedures (with formal

parameters) as appropriate

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Procedures

This technique is known as structuredprogramming. It

is characterized as

Modular(each procedure dedicated to one task which is

of limited and manageable size)

Has a Main-line procedure that controls program flow

by branching to the various sub-problem procedures

Single entryto, and single exitfrom, each procedure

GoTo-less code (not using the GoTo statement avoids

spaghetti code)

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Procedures

As we will see

We can debug each procedure independently, a much

simpler process than trying to debug a complexprogram as a whole

The procedures are reusable. We can combine a

procedure, as appropriate, with other procedures to

solve other problems

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Procedures

To call a procedure means to run (execute) it

When one procedure calls a second

The first procedure is the calling procedure; the second

procedure is the called procedure

VB first looks for the called procedure in the modulecontaining the calling procedure

if not found, it looks in all the other modules in the

workbookThere are two types of procedures

SUB procedures

FUNCTION procedures

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2. Sub Procedures

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Sub Procedures

A sub procedure performs a series of operationsand actions but does not return a value to thecalling procedure

Sub Name (arguments)CODE

End Sub

A sub procedure without arguments can be run onits own or be called by another procedure For example, it can be run from a worksheet by

selecting Macro from the Tools menu (Tools >> Macro>> Macros)

A sub procedure without arguments is known as a macro

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Sub Procedures

A sub procedure with arguments can only executewhen it is called by another procedure

Arguments are declared the same way as variables, butwithout the word Dim

If there is more than one argument, they are separatedby commas

The calling procedure passes values for the argumentsto the called procedure

Sub Name (X as Integer, Y as String, Z as Single)CODE

End Sub

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Sub Procedures

To call a sub procedure without arguments, useeither

Call Name

To call a sub procedure with arguments, use either

Call Name (Argument1, Argument2,.)

ie. Call FindMax (X, Y, Z)

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Sub Procedures

If you call a procedure that has arguments, as we

saw with algorithms,

The values of the arguments in the calling procedure

(the actual parameters) are passed to the arguments in

the called procedure (the formal parameters)

The arguments in the calling procedure may be

Constants, expressions or variables

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Sub Procedures

Sub Main()

'The calling procedure. Will show up on Tools Macro

Dim X as Integer

Dim Y as Single

Dim Z as Boolean

Call One (X, Y, Z) 'OK

Call One (X, Y) 'Not OK what about Z?

Call One (Y, Z, X) 'Not OK order is Int, Single, Boolean!

End Sub

Sub One (A as Integer, B as Single, C as Boolean)

'The called procedure. Will not show on the Tools menu

CODE

End Sub

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Sub Procedures

When the arguments in the calling procedure arevariables, the called procedure can change thevalueof these variables (passing by reference or

two-way passing), using the word ByRef If you want to avoid the possibility of the called

procedure changing the value of variables in thecalling procedure, preface the arguments in the

called procedure with the word ByVal(passingby value or one-way passing)

In either case, the number and type of argumentsin the calling statement must agree with those in

the called procedure

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Sub Procedures

Sub Main ()

Dim X as Integer

Dim Y as Single

X = 3

Y = 3.1

Call One (X, Y)

MsgBox (X = & X & Y = & Y)

End Sub

Sub One (ByRef A as Integer, ByVal B as Single)A = 9

B = 2.1

End Sub

Main One

X Y A B

3

3 3.1

33.1

9 3.1

9 2.1

9 3.1

Example 1

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Sub Procedures

Observe that we are not concerned about thepossibility of identical names for variables orarguments in the calling and called procedures

Since they are in separate procedures, even if a variableor argument name is identical in the two procedures,each is evaluated independently by Visual Basic (ie. asif they bear no relationship to one another)

This is why our procedure code is portable andreusable

However, we often want the called procedure toreturn a value

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3. Function Procedures

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Function Procedures

A function procedure performs a series ofoperations and returns a single valueFunction Name (arguments) as Type

CODEName = Expression

End Function

Observe that a function procedure will always

contain an assignment statement that assigns avalue to a variable with the name of the function

The type of that variable is defined in the functionheader line (as Type)

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Function Procedures

A function procedure is never run by itself. It is either

called from within another procedure or from a formula in

a worksheet cell

To call a function procedure from within another

procedure, use the function in an assignment statement

variable = Name(arguments)

For example, cells(6, 8) = Profit (us,pc,sp) calls the procedure

Function Profit(ByVal UnitsSold As Integer, ByVal ProdCost As Single, _

ByVal SalePrice As Single) As Single

Profit = UnitsSold * (SalePrice - ProdCost)

End Function

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Function Procedures

Z = Name (X, Y) a statement in the calling procedure

FunctionName (ByRef A as Integer, ByVal X as Single) as Integer

Name = ????

End Function

The variable X, an argument in the callingprocedure, is a different variable than the variableX, an argument in the called procedure

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Function Procedures

Sub Main ()

Dim X as Integer

Dim Y as Single

Dim Z as Boolean

X = 1

Y= 1.2

Z = Compare (X, Y)

MsgBox (X & Y & Z)

End Sub

Function Compare (ByRef A as Integer, ByVal B as Single) as Boolean

If (A > B) Then

Compare = True

ElseCompare = False

End If

A = 3

B = 2.4

End Function

Main CompareX Y Z || A B Compare1 1.2 ||

|| 1|| 1.2|| F|| 3

|| 2.43 1.2 F ||

Example 2

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Function Procedures

a function procedure can be entered in a worksheetcell as a formula ie. called from a worksheet The function procedure is then known as a user defined

function It must be entered in a module code window

If it is entered in a worksheet code window (right click sheettab and select View code), it cannot be called from a worksheet

If the formula in cell A1 is =Compare(B1,C1)

Cell A1 would contain a True if the value in B1 isgreater than the value in C1. Otherwise, cell A1 wouldcontain False

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Translate 19 see 17.vb_5.xls

Translate algorithm 5.1 into Visual Basic using theworksheet CSI1234

Name is in column A

Midterm mark is in column B Final exam mark is in column C

Final mark is in column D

Data starts in row 3

The algorithm is to find the number of studentswith a final mark greater than the average finalmark

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Algorithm 5.1

Putting it all together

Name: AVGLGivens :L, N

Change: NoneResult : AvgIntermediates: Sum, I

DefinitionAvg := AVGL(L, N)

Get L, N

Let Sum = 0

Let I = 1

Loop When (I

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Algorithm 5.1

Our algorithms AVGL & COUNTL process data

in a list L of length N.

Lets rewrite them to process data in a list on a

worksheet (WS) starting at a particular row (Row)

of column (Col) and ending at the first blank cell

in that column.

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Algorithm 5.1

Name: AVGLGivens: L, N

Change: NoneResults: AvgIntermediates: Sum, IDefinitionAvg := AVGL(L, N)

Get L, N

Let Sum = 0

Let I = 1

Loop When (I

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Algorithm 5.1

Now, lets translate the algorithm into a Visual

Basic function procedure so that it can be called

from another procedure or from a formula in a

worksheet.

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Algorithm 5.1

Name: AVGLGivens: Row, Col

Change: NoneResults : AvgIntermediates: Sum, Count, ValueDefinitionAvg := AVGL(Row, Col)

Get Row, Col

Let Sum = 0

Let Count = 0

Loop until empty cell

Get Value(Row,Col)Let Sum = Sum + Value

Let Count = Count + 1

Let Row = Row + 1

Finish Loop

Let Avg = Sum/Count

Give Avg

Function AVGL(ByVal Row As Integer, _ByVal Col as Integer) As Single

Dim Sum as Single

Dim Value as Single

Dim Count as Integer

Dim Avg as Single

Sum = 0Count = 0

Do Until (IsEmpty(Cells(Row, Col)))

Value = Cells(Row, Col)

Sum = Sum + Value

Count = Count + 1

Row = Row + 1Loop

Avg = Sum/Count

AVGL = Avg

End Function

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Algorithm 5.1

Applying the same process to COUNTL produces

the following function procedure.

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Algorithm 5.1

Name: COUNTLGivens: Col, Row, V, Value

Change: NoneResult: CountIntermediate:DefinitionCount := COUNTL(Row, Col, V)

Get Row, Col, V

Let Count = 0

Loop until empty cell

Get Value(Row,Col)If (Value > V)

Let Count = Count + 1

Row = Row + 1

Finish Loop

Give Count

Function CountL(ByVal Row As Integer,ByVal Col As Integer, ByVal V AsSingle) As Integer

Dim Value As Single

Dim Count As Integer

Count = 0

Do Until IsEmpty(Cells(Row, Col))

Value = Cells(Row, Col)

If (Value > V) Then

Count = Count + 1End If

Row = Row + 1

Loop

CountL = Count

End Function

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Name: MAINGivens: Marks, NStu

Change: NoneResults: NGoodIntermediate: AMarkDefinitionNGood:=MAIN(Marks,Nstu)

Get Marks, NStu

AMark := AVGL(Marks,NStu)NGood := COUNTL(Marks,NStu, AMark)

Give NGood

Sub Main()

Dim Col as Integer

Dim Row As Integer

Dim Ngood as Integer

Dim AMark as Single

Worksheets(CSI1234).Activate

Row = 3

Col = 4

Amark = AVGL(Row, Col)

Ngood = COUNTL(Row, Col, Amark)MsgBox(Ngood & >Avg)

End Sub

Algorithm 5.1

Name: MAINGivens: Row, Col, WS

Change: NoneResults: NGoodIntermediate: AMarkDefinitionNGood:=MAIN(Row, Col, WS)

Go to Worksheet WS

AMark := AVGL(Row, Col)

NGood := COUNTL(Row, Col, AMark)

Give NGood

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Algorithm 5.1

Function AVGL(ByVal Row _

As Integer, ByVal Col As _

Integer) As Single

Dim Sum As Single

Dim Value As Single

Dim Count As IntegerSum = 0

Count = 0

Do Until IsEmpty(Cells(Row, _

Col))

Value = Cells(Row, Col)

Sum = Sum + Value

Count = Count + 1

Row = Row + 1

Loop

AvgL = Sum / Count

End Function

Function COUNTL(ByVal _

Row As Integer, ByVal Col As _

Integer, ByVal V As Single) As _

Integer

Dim Value As Single

Dim Count As Integer

Count = 0

Do Until IsEmpty(Cells(Row, _

Col))

Value = Cells(Row, Col)

If (Value > V) Then

Count = Count + 1

End IfRow = Row + 1

Loop

CountL = Count

End Function

Sub Main()

Dim Col as Integer

Dim Row As Integer

Dim Ngood as Integer

Dim AMark as Single

Worksheets("CSI1234").Activate

Row = 3

Col = 4

Amark = AVGL(Row, Col)

NGood = COUNTL(Row, _Col, Amark)

MsgBox(Ngood & ">Avg")

End Sub

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Translate 20 see 17.vb_5.xls

Use algorithm 5.4 to find how many ties there

were for the maximum grade in CSI1234

Name is in column A

Midterm mark is in column B

Final exam mark is in column C

Final mark is in column D

Data starts in row 3 and ends in row 20

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CMAX

(01) Get L, N

(02) Max := MAXL(L,N)

(03) Nmax :=

SEARCHK(L,N,Max)

(04) Give NMax

MAXL(11) Get L, N(12) Max = -1(13) I = 1(14) Loop When (I Max)

(16) Max = LI

(17) I = I + 1(18) Finish Loop(19) Give Max

COUNTk(21) Get L, N, K(22) C = 0

(23) I = 1(24) Loop When (I Max) Then

Max = Value

End If

Next Row

End Sub

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CMAX

(01) Get L, N

(02) Max := MAXL(L,N)

(03) Nmax :=

SEARCHK(L,N,Max)

(04) Give NMax

MAXL(11) Get L, N(12) Max = -1(13) I = 1(14) Loop When (I Max)

(16) Max = LI

(17) I = I + 1(18) Finish Loop(19) Give Max

COUNTk(21) Get L, N, K(22) C = 0

(23) I = 1(24) Loop When (I

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Homework

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When and where do you use each of the following?

Dim x As Integer

ByRef x As Integer

ByVal x As Integer

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Write a sub procedure that takes one parameter and producesa message box that says The argument sent to me was: and then displays the value of the parameter. Now write asub procedure that calls this procedure.

Create a function procedure that uses several arguments andreturns a value based on a calculation. Write a sub

procedure that calls this function procedure.

Write a sub procedure that consists entirely of calls to otherprocedures. Use at least three procedure calls, onefunction procedure, one sub procedure and one requiringarguments. Now write the procedures that it calls.