CSI 1306
PROGRAMMING IN VISUAL BASIC
PART 5
Part 5
 1. Procedures
 2. Sub Procedures
 3. Function Procedures
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 single
module
 Many modules can be added to a single workbook
– To add a new module to a workbook, select Module
from the Insert menu
Procedures
 To simplify solving a problem, we
– Divide the problem into a number of smaller problems,
and
– Develop an algorithm for each of these smaller
problems, then
– Develop a main algorithm (with actual parameters) that
assembles the algorithms (with formal parameters) as
appropriate to solve the problem
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
Procedures
 This technique is known as structured programming. 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 entry to, and single exit from, each procedure
“GoTo-less” code (not using the GoTo statement avoids
spaghetti code)
Procedures
 As we will see
– We can debug each procedure independently, a much
simpler process than trying to debug a complex
program as a whole
– The procedures are reusable. We can combine a
procedure, as appropriate, with other procedures to
solve other problems
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 module
containing the calling procedure
– if not found, it looks in all the other modules in the
workbook
 There are two types of procedures
– SUB procedures
– FUNCTION procedures
2. Sub Procedures
Sub Procedures
 A sub procedure performs a series of operations
and actions but does not return a value to the
calling procedure
Sub Name (arguments)
CODE
End Sub
 A sub procedure without arguments can be run on
its 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
Sub Procedures
 A sub procedure with arguments can only execute
when it is called by another procedure
– Arguments are declared the same way as variables, but
without the word Dim
– If there is more than one argument, they are separated
by commas
– The calling procedure passes values for the arguments
to the called procedure
Sub Name (X as Integer, Y as String, Z as Single)
CODE
End Sub
Sub Procedures
 To call a sub procedure without arguments, use
either
Call Name
 To call a sub procedure with arguments, use either
Call Name (Argument1, Argument2,….)
• ie. Call FindMax (X, Y, Z)
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
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
Sub Procedures
 When the arguments in the calling procedure are
variables, the called procedure can change the
value of 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 the
calling procedure, preface the arguments in the
called procedure with the word ByVal (passing by
value or one-way passing)
 In either case, the number and type of arguments
in the calling statement must agree with those in
the called procedure
Sub Procedures
Call Name (X, Y)
‘a statement in the calling procedure
Sub Name (ByRef A as Integer, ByVal B as Integer)
‘the header for the called procedure
Sub Procedures
Main
X Y
3
3 3.1
3
Sub Main ()
Dim X as Integer
Dim Y as Single
X = 3
Y = 3.1
One
A
B
9
9
9
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
Example 1
3.1
3.1
2.1
Sub Procedures
 Observe that we are not concerned about the
possibility of identical names for variables or
arguments in the calling and called procedures
– Since they are in separate procedures, even if a variable
or argument name is identical in the two procedures,
each is evaluated independently by Visual Basic (ie. as
if they bear no relationship to one another)
 This is why our procedure code is portable and
reusable
 However, we often want the called procedure to
return a value
3. Function Procedures
Function Procedures
 A function procedure performs a series of
operations and returns a single value
Function Name (arguments) as Type
CODE
Name = Expression
End Function
 Observe that a function procedure will always
contain an assignment statement that assigns a
value to a variable with the name of the function
 The type of that variable is defined in the function
header line (as Type)
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
Function Procedures
Z = Name (X, Y) ‘a statement in the calling procedure
Function Name (ByRef A as Integer, ByVal X as Single) as Integer
Name = ????
End Function
 The variable X, an argument in the calling
procedure, is a different variable than the variable
X, an argument in the called procedure
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
X
1
3
Main
Compare
Y
Z || A B Compare
1.2
||
|| 1
||
1.2
||
F
|| 3
||
2.4
1.2 F ||
Function Compare (ByRef A as Integer, ByVal B as Single) as Boolean
If (A > B) Then
Compare = True
Else
Compare = False
End If
A = 3
B = 2.4
End Function
Example 2
Function Procedures
 a function procedure can be entered in a worksheet
cell 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 sheet
tab 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 is
greater than the value in C1. Otherwise, cell A1 would
contain False
Translate 19 see 17.vb_5.xls
 Translate algorithm 5.1 into Visual Basic using the
worksheet 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 students
with a final mark greater than the average final
mark
Algorithm 5.1
 Putting it all together
Name: AVGL
Givens :L, N
Change: None
Result : Avg
Intermediates: Sum, I
Definition
Avg := AVGL(L, N)
Name: COUNTL
Givens: L, N, V
Change: None
Result: Count
Intermediate: I
Definition
Count := COUNTL(L, N, V)
Get L, N
Let Sum = 0
Let I = 1
Loop When (I <= N)
Let Sum = Sum + LI
Let I = I + 1
Finish Loop
Let Avg = Sum/N
Give Avg
Get L, N, V
Let Count = 0
Let I = 1
Loop When (I <=N)
If (LI > V)
Let Count = Count + 1
Let I = I + 1
Finish Loop
Give Count
Name: MAIN
Givens: Marks, NStu
Change: None
Result: NGood
Intermediate: AMark
Definition
NGood:=MAIN(Marks,Nstu)
Get Marks, NStu
AMark := AVGL(Marks,NStu)
NGood := COUNTL(Marks,
NStu, AMark)
Give NGood
Algorithm 5.1
 Our algorithms AVGL & COUNTL process data in
a list L of length N.
 Let’s 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.
Algorithm 5.1
Name: AVGL
Givens: L, N
Change: None
Results: Avg
Intermediates: Sum, I
Definition
Avg := AVGL(L, N)
Get L, N
Let Sum = 0
Let I = 1
Loop When (I <= N)
Let Sum = Sum + LI
Let I = I + 1
Finish Loop
Let Avg = Sum/N
Give Avg
Name: AVGL
Givens: Row, Col
Change: None
Results : Avg
Intermediates: Sum, Count, Value
Definition
Avg := 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
Algorithm 5.1
 Now, let’s 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.
Algorithm 5.1
Name: AVGL
Givens: Row, Col
Change: None
Results : Avg
Intermediates: Sum, Count, Value
Definition
Avg := 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 = 0
Count = 0
Do Until (IsEmpty(Cells(Row, Col)))
Value = Cells(Row, Col)
Sum = Sum + Value
Count = Count + 1
Row = Row + 1
Loop
Avg = Sum/Count
AVGL = Avg
End Function
Algorithm 5.1
 Applying the same process to COUNTL produces
the following function procedure.
Algorithm 5.1
Name: COUNTL
Givens: Col, Row, V, Value
Change: None
Result: Count
Intermediate:
Definition
Count := 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 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 If
Row = Row + 1
Loop
CountL = Count
End Function
Algorithm 5.1
Name: MAIN
Givens: Marks, NStu
Change: None
Results: NGood
Intermediate: AMark
Definition
NGood:=MAIN(Marks,Nstu)
Get Marks, NStu
AMark := AVGL(Marks,NStu)
Sub Main()
Dim Col as Integer
Dim Row As Integer
Dim Ngood as Integer
Dim AMark as Single
NGood := COUNTL(Marks,NStu, AMark)
Give NGood
Name: MAIN
Givens: Row, Col, WS
Change: None
Results: NGood
Intermediate: AMark
Definition
NGood:=MAIN(Row, Col, WS)
Go to Worksheet WS
AMark := AVGL(Row, Col)
NGood := COUNTL(Row, Col, AMark)
Give NGood
Worksheets(“CSI1234”).Activate
Row = 3
Col = 4
Amark = AVGL(Row, Col)
Ngood = COUNTL(Row, Col, Amark)
MsgBox(Ngood & “>Avg”)
End Sub
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 Integer
Sum = 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 If
Row = 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
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
CMAX
(01) Get L, N
(02) Max := MAXL(L,N)
(03) Nmax :=
SEARCHK(L,N,Max)
(04) Give NMax
MAXL
(11) Get L, N
Sub Cmax()
(12) Max = -1
Dim FinCol as Integer
(13) I = 1
(14) Loop When (I <= N)
Dim MaxFin as Single
(15)
If (LI > Max)
Dim CFin as Integer
(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 <= N)
(25)
If (LI = K)
(26)
C=C+ 1
(27)
I=I+1
(28) Finish Loop
(29) Give C
Worksheets("CSI1234").Activate
FinCol = 4
Call MaxL(FinCol, MaxFin)
Call CountK(FinCol, MaxFin, Cfin)
MsgBox(Cfin & " Tied For Max")
End Sub
CMAX
(01) Get L, N
(02) Max := MAXL(L,N)
Sub MaxL (ByVal Col as Integer, _
(03) Nmax :=
ByRef Max as Single)
SEARCHK(L,N,Max)
Dim Row as Integer
(04) Give NMax
MAXL
(11) Get L, N
(12) Max = -1
(13) I = 1
(14) Loop When (I <= N)
(15)
If (LI > 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 <= N)
(25)
If (LI = K)
(26)
C=C+ 1
(27)
I=I+1
(28) Finish Loop
(29) Give C
Dim Value as Single
Const FirstRow = 3
Const LastRow = 20
Max = -1
For Row = FirstRow to LastRow
Value = Cells(Row, Col)
If (Value > Max) Then
Max = Value
End If
Next Row
End Sub
CMAX
Sub COUNTK (ByVal Col as Integer, _
(01) Get L, N
(02) Max := MAXL(L,N)
ByVal V as Single, _
(03) Nmax :=
ByRef C as Integer)
SEARCHK(L,N,Max)
Dim Row as Integer
(04) Give NMax
MAXL
(11) Get L, N
(12) Max = -1
(13) I = 1
(14) Loop When (I <= N)
(15)
If (LI > 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 <= N)
(25)
If (LI = K)
(26)
C=C+ 1
(27)
I=I+1
(28) Finish Loop
(29) Give C
Dim Value as Single
Const FirstRow = 3
Const LastRow = 20
C = 0
For Row = FirstRow to LastRow
Value = Cells(Row, Col)
If (Value = V) Then
C = C + 1
End If
Next Row
End Sub
Homework
When and where do you use each of the following?
Dim x As Integer
ByRef x As Integer
ByVal x As Integer
Write a sub procedure that takes one parameter and produces
a message box that says “The argument sent to me was: “
and then displays the value of the parameter. Now write a
sub procedure that calls this procedure.
Create a function procedure that uses several arguments and
returns 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 other
procedures. Use at least three procedure calls, one
function procedure, one sub procedure and one requiring
arguments. Now write the procedures that it calls.