Database Management Systems
Chapter 7
Calculations and Data
Manipulation
Jerry Post
Copyright © 1998
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Database Programming









Variables
Computations
Standard Functions
Debug
Output
Input
Conditions
Loops
Arrays









Data on Forms
Properties
Events
DoCmd: Internal Commands
Data Transfer Across Forms
Data Lookup
Programming SQL
Database access programming
Functions & statements grouped
by task
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Programming Environment
 Create code
Tables
 (1) In forms and reports
 (2) Within the query system
 (3) Hosted in external programs
External
Program (3)
DBMS
Queries
(2)
Forms &
Reports
If ( . . ) Then
SELECT . . .
Else . . .
UPDATE . . .
End If
C++
if (. . .) {
// embed SQL
SELECT …
}
(1)
If (Click) Then
MsgBox . . .
End If
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Programming
Appendix
Windows Environment
 Before Windows
 Your code did all of the
work.
 Programmer In complete
control.
 Code ran from top to
bottom.
Monolithic Code
Start here
Do this routine
If (. . .) Then
print . . .
End If
Wait for input
More routines
End here
 With Windows
 Structure and interface are
defined by Windows
standards.
 Event-driven. Code is in
small pieces that are called
as needed, when some
event occurs.
Windows Form
Event/Trigger
On_Click
MsgBox . . .
On_Change
UPDATE . . .
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Data on Forms
 Simple assignment
 [control] = value
 value = [control]
 Naming conventions
 Is it a variable or a control?
 Full names
 Forms![myform]![ctlTax]
 Null values:
 IsNull([control])
Form
32.50
ctlTax
Code
Sub ComputeTax
Total = …
taxRate = ...
[ctlTax] = taxRate*Total
End Sub
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Control Properties and Methods
 Set properties with code
 Examples
Employee
 Visible/Invisible
 Locked/Unlocked
 Combo box RowSource
 Methods
 SetFocus
 Undo
 Requery
 Code examples




[control].Visible = False
[control].Locked = False
[control].SetFocus
[combo].RowSource=
“SELECT ... FROM . . .”
Sub Employee_AfterUpdate()
If (Employee = “manager”) Then
[cmdSalary].Visible = True
[cmdSchedule].Visible = True
Else
[cmdSalary].Visible = False
[cmdSchedule].Visible = False
End If
End Sub
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Transfer Data Across Forms
 Full names:
 Forms!
 [formname1]!
 [control1]
 Forms must be open
 Form1.Visible = True
 Subforms:




Forms!
[formname1]!
[subform].Form!
[control1]
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Common Properties
 Forms







Record Source
Caption
Default View
Menu/Scroll Bars
Navigation/Selection
Size/Center
Pop Up/Modal/Border
 Controls
 Name
 Control Source
 Format/Decimal/Default
 Controls











Input Mask
Validation Rule/Text
Status Bar
Auto Tab/Enter
Visible
Enabled/Locked
Tab Stop/Index
Size, Position
Back/Fore Color/Effects
Border
Font
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Common Events
 Forms











Current
Before/After Insert
Before/After Update
Delete
Before/After Del Confirm
Open/Close
Load/Unload
Activate/Deactivate
Got/Lost Focus
Click/Double Click
Error/Timer
 Controls








Before/After Update
Change
Enter/Exit
Got/Lost Focus
Click
Double Click
Mouse
Key Down/Up/Press
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DoCmd: Internal Commands
 See help system
 Common uses



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


FindNext
FindRecord
GoToControl
GoToPage
GoToRecord
Hourglass
Maximize/Minimize










OpenForm
OpenQuery
OpenReport
Print
Quit
RunApp (Shell)
RunSQL
SetWarnings
TransferDatabase
TransferSpreadsheet
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Programming: SQL
 Select Into
 New table
 Insert Into
 Operate on sets of data
 Use String for Where
 Use DoCmd RunSQL
 Append rows
 Update
 Change data
 Delete
 Delete rows
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Update
 Changes set of values--based on Where
 Syntax
 Update table SET col1=val1, col2=val3 Where condition
 Examples
 strSQL = “Update Order Set EstShipDate=OrderDate+3”
 DoCmd RunSQL strSQL
 strSQL = “Update Product Set Price = Price*”
 strSQL = strSQL & CStr(1.0 + [ctlIncrease])
 strSQL = strSQL & “ Where “ & [ctlWhere]
 DoCmd RunSQL strSQL
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SQL Example: Employee Titles
 Employee Table
 Change titles




EID
2298
9983
2736
Create a form
Old title (combo)
New title
Command button
Name
Adams
Cuervo
Dubai
Phone
2253
9973
3385
Title
Manager
Supervisor
Worker
Manager
Team Leader
Go
 SQL
UPDATE Employee
SET Title = " Team Leader "
WHERE Title = " Manager ”;
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SQL Example: New Titles
UPDATE Employee
SET Title = "Team Leader"
WHERE Title = "Manager";
Manager
Team Leader
Go
Sub cmdGo_AfterUpdate
Build Update command in a String,
using values from OldTitle and NewTitle.
Execute the command.
End Sub
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Build the SQL Update Command
Sub cmdGo_AfterUpdate
Dim strSQL As String
strSQL = "UPDATE Employee SET Title = ” & txtNewTitle
& " WHERE Title = ” & cboOldTitle
_
End Sub
strSQL:
UPDATE Employee SET Title = Team Leader
WHERE Title = Manager
Problem: You need quotation marks around the titles.
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SQL Update Example
SQL
Sample
UPDATE Employee SET Title = "“Team Leader "
WHERE Title = "Manager";
Sub cmdGo_AfterUpdate
Dim strSQL As String, q as String
q = Chr(34) ‘ quotation mark
strSQL = "UPDATE Employee SET Title = " & q & [txtNewTitle] & q
& " WHERE Title = " & q & [cboOldTitle] & q & " ; "
DoCmd.SetWarnings False
DoCmd.RunSQL strSQL
DoCmd.SetWarnings True
_
‘ Turn off warnings
‘ Execute the SQL command
End Sub
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Debug your Query
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Insert Into (1)
 Adds rows to a table
 Syntax
 Insert Into table (col1, col2, …)
 Values (value1, value2, …
LastName FirstName
Masi
Jorge
CID Last
…
938 Sosa
Masi
First
Phone
Javier 8474
Jorge
strSQL = “Insert Into [Customer] (Last, First)”
strSQL = strSQL & “ Values (“ & “””” & [ctlLast] & “”””
strSQL = strSQL & “,” & “””” & [ctlFirst] & “””” & “)”
DoCmd RunSQL strSQL
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Insert Into (2)
 Copies data rows to a second table
 Syntax
 INSERT INTO {new table, columns}
SELECT {any SQL}
 Example, move all customers who have
not placed orders recently.
 Let users define “recently” by picking the
number of days.
SQL
INSERT INTO OldCustomer
SELECT * FROM Customer
WHERE CustomerID NOT IN
(SELECT CustomerID
FROM Order
WHERE (Odate > Date() - x);
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Code Example for Insert
CustomerID
7763
3635
4456
O#
9987
2275
Name Phone
Juarez 9987
Kramer 2285
Ciaro 8474
C#
3635
4456
Odate
02-15-98
05-23-98
CustomerID Name Phone
7763
Juarez 9987
…
Customers who have not
placed an order within some
time frame.
Dim strSQL
strSQL = “INSERT INTO OldCustomer”
strSQL = strSQL & “ SELECT * FROM Customer WHERE”
strSQL = strSQL & “ CustomerID NOT IN”
strSQL = strSQL & “ (SELECT CustomerID FROM Order”
strSQL = strSQL & “ WHERE (Odate > Date() - “
strSQL = strSQL & [txtDays] & “);”
Time frame (txtDays)
DoCmd.RunSQL strSQL
is given by user.
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Delete




Delete a set of rows that match a condition
Syntax: Delete From table Where condition
Cascade on Delete!
Example: Move old customer data
strWhere = “CustomerID NOT IN (SELECT CustomerID FROM Order”
strWhere = strWhere & “ WHERE (Odate > Date() - “ & [txtDays] & “);”
strSQL = “INSERT INTO OldCustomer”
strSQL = strSQL & “ SELECT * FROM Customer WHERE “ & strWhere
DoCmd.RunSQL strSQL
‘ Copy old customer data
‘ To Do: Backup the data in related tables
strSQL = “DELETE FROM Customer WHERE “ & strWhere
DoCmd.RunSQL strSQL
‘ Delete from main table & cascade
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Data Lookup Commands: D...
 Syntax
 D... (expr, domain, criteria)
 “Column”
 “Table”
 “Where Clause”
 Functions





DAvg, DCount, DFirst,
DLast, DMin, DMax,
DStDev, DStDevP,
DSum, DVar, DVarP
Dlookup
Column
Table
V = DSum(“BalanceDue”, “Customer”,
“City=‘Chicago’”)
Where Clause
 Usually better to use SQL.
 Or to write DAO code.
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Data Access Object Programming
 Purpose
 Track through table or query
one row at a time.
 Data cursor/pointer to active
row.
 Why?
 Performance.
 SQL cannot do everything.
 Complex calculations.
 Compare multiple rows.
Year
1995
1995
1996
1997
1998
Sales
104,321
104,321
145,998
276,004
362,736
MoveNext
MovePrevious
MoveFirst
MoveLast
Move
Test for Beginning
and End of File
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Data Access Object Programming
 Containers
 DBEngine
 Workspaces
 Databases
 Recordsets
 Read
 Write
DBEngine
Workspace
Database
Recordset (query)
Dim dbs As Database
Dim rst As Recordset
Set dbs = CurrentDB()
Set rst = dbs.OpenRecordset(“my query”)
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Program Structure
Set dbs = CurrentDB()
Choose the database
strSQL = “SELECT … “
Define the query
Set rst = dbs.OpenRecordset(strSQL) Open the query to the first row
Do Until (rst.EOF)
Read or Write data
in the current row
rst.MoveNext
Loop
rst.Close
Loop through the query
Read data
or make changes
Go to the next row
Repeat
Close the query
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Problems with Multiple Users
Original Data
Modified Data
Name
Alice
Carl
Donna
Ed
Name
Alice
Neal
Carl
Donna
Ed
Sales
444,321
254,998
652,004
411,736
New row is
added--while
code is running.
Sales
444,321
333,229
254,998
652,004
411,736
Set rst = dbs. OpenRecordset(“Data”)
Value1 = rst!Sales
‘ Alice (444,321)
rst.MoveNext
‘ Carl
…
rst.MovePrevious
‘ ??? Which row
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Table Locator Commands
 Move Commands





 Bookmarks
 Dim MyMark As String
 MyMark = rst.Bookmark
.MoveNext
.MovePrevious
.MoveFirst
.MoveLast
.Move nRows
 (Save position)
 .Move . . .
 (Move somewhere else)
 rst.Bookmark = MyMark
 Location tests
 BOF
 EOF
Name
Alice
Neal
Carl
Donna
Ed
 (Return to mark)
Sales
444,321
333,229
254,998
652,004
411,736
Save
position
bmk = rst.Bookmark
rst.MoveNext
rst.Bookmark = bmk
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Recordset Find Commands






.FindFirst “condition”
.FindLast “condition”
.FindNext “condition”
.FindPrevious “condition”
Inefficient: Sequential search
Use SQL instead
rst.Index = “PrimaryKey”
 rs.NoMatch
 rs.Seek
 Indexed
 One item
rst.Seek “=“, keyvalue
If (rst.NoMatch = False) Then
‘ Make changes
End If
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Sample Data Access Code
Dim dblSum As Double
Dim dbs As Database
Dim rst As Recordset
Set dbs = CurrentDB()
Set rst = dbs.OpenRecordset(“Customer”)
dblSum = 0.0
Do Until (rst.EOF)
dblSum = dblSum + rst!BalanceDue
rst.MoveNext
Loop
rst.Close
MsgBox “Total Due = “ & dblSum
Compute total of
BalanceDue.
Normally use SQL instead.
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Sample Code to Change Data
Dim dbs As Database
Dim rst As Recordset
Do Until (rst.EOF)
rst.Edit
rst!BalanceDue = rst!BalanceDue*(1 + [PctIncrease] )
rst.Update
rst.MoveNext
Loop
rst.Close
Add a 10% charge to the BalanceDue
for every customer. The 10% value is
entered on the form by the user.
What happens if the row is already locked?
Normally use SQL instead.
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Error Handling
 Errors are events
 Simple code:
 Event Options
 Display error and exit
 MsgBox Err.Description, ,
“Title”
 Resume Exit_Label
 On Error Goto [label]
 On Error Goto 0
 On Error Resume Next
 Resume Options
On Error Goto ErrSub1
Program code
ExitSub1:
Exit Sub
 Resume
 Resume Next
 Resume label
Error occurs
ErrSub1:
MsgBox Err.Description,,”Errors”
Resume ExitSub1
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Alternate Error Handling
Sub mySubroutine
On Error Resume Next
…
Set rst=dbs.OpenRecordset(“data”)
If IsNull(rst) Then
… Handle the error
End If
Error occurs,
skip to next line.
Test for error,
handle it.
Exit Sub
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Concurrent Access
 Concurrent Access
 Two processes
 Multiple users or
processes changing the
same data at the same
time.
 Final data will be wrong!
 Force sequential
 Locking
 Delayed, batch updates
Receive Payment
1) Read balance
2) Subtract pmt
4) Save new bal.
800
-200
600
 Receive payment ($200)
 Place new order ($150)
 Initial balance $800
 Result should be $800 200 + 150 = $750
 Interference result is
either $600 or $950
Customers
ID
Jones
Balance
$800
$600
$950
Place New Order
3) Read balance
5) Add order
6) Write balance
800
150
950
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Deadlock
 Deadlock
 Two (or more) processes have
placed locks on data and are
waiting for the other’s data.
1) Lock Data A
3) Wait for Data B
 Many solutions
 Random wait time
 Global lock manager
 Two-phase commit - messages
Data A
Data B
2) Lock Data B
4) Wait for Data A
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Lock Manager
Resource
A
Process1
Process2
Resource
B
Lock
Wait
Process7
Resource
E
Lock
Wait
Lock
Wait
Process5
Process6
Resource
D
Wait
Lock
Process3
Process4
Resource
C
Wait
Lock
Wait
Wait
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Concurrent Access
Customer
Using & Adams
locked Brown
Jones
Balance
152.35
315.81
115.67
Running the program to add interest
charges generates an error message.
Do until rst.EOF
rst.Edit
rst!Balance = rst!Balance*(1.0+rate)
rst.Update
rst.MoveNext
Loop
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Errors and Locks
On Error Goto ErrSub1
…
rst.Edit
rst!Balance = rst!Balance*1.10
rst.Update
…
ExitSub1:
Exit Sub
If the table is locked,
Edit will cause an error.
ErrSub1:
If ( MsgBox (Err.Description, VbRetryCancel,
"Error (RS)” ) = vbRetry ) Then
Resume
Let the user retry the edit or exit.
Else
To do it automatically, wait
Resume ExitSub1
for a random number of seconds.
End If
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Post’s Picky Programming
• Use a naming convention.
• Use proper indentation.
• Comment your work.
• Avoid spaces in variable names.
• Use Option Explicit.
• Recompile constantly.
• Use as many parentheses as possible.
• Split complex conditions.
• Make it easy for the user.
• Use the status bar and tool tips.
• All code must be subject to error trapping.
• Use Retry with rst.Edit sections.
• Use subroutines and functions to simplify.
• Keep backup copies.
• Never use a raw number--use Const.
• Remember that databases can be moved.
• Test applications on different hardware.
•Test all calculations by hand.
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Comments
dblSum = 0#
Do While Not rst.EOF
dblSum = dblSum + rst!Balance
rst.MoveNext
Loop
Weak comments
' Initialize the accumulator
' Loop through the table
' Accumulate the balance
' Move to the next row
' End the loop
' Need to compute total balance from sales
Useful comments
' Will use a loop instead of SQL
' Because some conditions will be added later
dblSum = 0#
Do While Not rst.EOF
' Add condition when user provides it, for example
' If this customer has more than three sales past due,
' only count the three most recent (write off the older ones)
dblSum = dblSum + rst!Balance
rst.MoveNext
Loop
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Sally’s Pet Store
Main Switchboard
Employee logs in.
Buttons are presented
based on the management
level of the employee.
Accounting
Marketing
Employees
Not available
to this employee.
Purchasing forms
are accessible by
this employee.
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Sally’s Pet Store: Switchboard Logic
Event: EmployeeID AfterUpdate
On Error Goto ErrEIDAU
Declare variables.
Lookup assigned ManagementLevel of employee.
Get Management levels for each section.
Make two sections of buttons invisible.
If (MgtLevel > Level1) Then
Make first section of buttons visible.
If (MgtLevel > Level2) Then
make second section of buttons visible.
End If
End If
ExitEIDAU:
Exit Sub
ErrEIDAU:
MsgBox
Resume ExitEIDAU
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Sally’s Pet Store: Switchboard Code
Private Sub EmployeeID_AfterUpdate()
On Error GoTo ErrEIDAU
Dim varLevel, varMGTLEVEL1, varMGTLEVEL2
If Not IsNull(EmployeeID) Then
varLevel = DLookup("EmployeeLevel", "Employee", _
"EmployeeID=" & [EmployeeID])
If Not IsNull(varLevel) Then
varMGTLEVEL1 = DLookup("Value", "Preferences", _
"KeyID=" & """" & "MGTLEVEL1" & """")
varMGTLEVEL2 = DLookup("Value", "Preferences", _
"KeyID=" & """" & "MGTLEVEL2" & """")
End If
End If
cmdAnimalPurchase.Visible = False
cmdMerchandisePurchase.Visible = False
cmdInventory.Visible = False
cmdAccounting.Visible = False
cmdMarketing.Visible = False
cmdEmployees.Visible = False
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Sally’s Pet Store: Switchboard Code
If (varLevel > Val(varMGTLEVEL1)) Then
cmdAnimalPurchase.Visible = True
cmdMerchandisePurchase.Visible = True
cmdInventory.Visible = True
If (varLevel > Val(varMGTLEVEL2)) Then
cmdAccounting.Visible = True
cmdMarketing.Visible = True
cmdEmployees.Visible = True
End If
End If
ExitEIDAU:
Exit Sub
ErrEIDAU:
MsgBox Err.Description, , "Unexpected Error (EIDAU)"
Resume ExitEIDAU
End Sub
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Sally’s Pet Store: Employees
Enter a ZIP code and the form
tries to find a matching city.
Choose a city and the ZIP code
is entered automatically.
Spin buttons can be used
to set employee level.
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Sally’s Pet Store: Employee Spin Button
Private Sub SpinLevel_SpinDown()
If IsNull(EmployeeLevel) Then
EmployeeLevel = 0
Else
If (EmployeeLevel > 0) Then EmployeeLevel = EmployeeLevel - 1
End If
End Sub
Private Sub SpinLevel_SpinUp()
If IsNull(EmployeeLevel) Then
EmployeeLevel = 1
Else
If (EmployeeLevel < 255) Then EmployeeLevel = EmployeeLevel + 1
End If
End Sub
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Sally’s Pet Store: City
Private Sub CityID_AfterUpdate()
On Error GoTo ErrCIDAU
‘ Requires a large city table.
If IsNull([ZipCode]) Then
[ZipCode] = DLookup("ZipCode", "City", "CityID=" & [CityID])
End If
‘ Do not replace an existing ZipCode entry.
ExitCIDAU:
Exit Sub
ErrCIDAU:
MsgBox Err.Description, , "Unexpected Error (CIDAU)"
Resume ExitCIDAU
End Sub
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Sally’s Pet Store: ZipCode
Private Sub Zipcode_AfterUpdate()
On Error GoTo ErrZCAU
Dim strZipShort As Variant, newCityID As Variant
strZipShort = Get5DigitZipCode(ZipCode)
newCityID = DLookup("CityID", "City", _
"ZipCode=" & """" & strZipShort & """")
If Not IsNull(newCityID) Then
[CityID] = newCityID
End If
‘ City table only uses 5 digit codes.
ExitZCAU:
‘ But we need to store 9 digits in ZipCode.
Exit Sub
ErrZCAU:
MsgBox Err.Description, , "Unexpected Error (ZCAU)"
Resume ExitZCAU
End Sub
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Programming Review: Variables
 Integer
 2 bytes
 -32768 32767
 Long
 4 bytes
 +/- 2,147,483,648
 Single
 4 bytes
 +/- 3.402823 E 38
 +/- 1.401298 E-45
 Global, Const, Static
 Double
 8 bytes
 +/- 1.79769313486232 E 308
 +/- 4.94065645841247 E-324
 Currency
 8 bytes
 +/- 922,337,203,685,477.5808
 String & String*n
 Variant
 Any data type
 Null
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Programming: Scope and Lifetime
 Scope
 Where is the variable, and
which procedures can
access it?
 Lifetime
 When is the variable
created, and when is it
destroyed?
Different procedures,
different variables.
Created and destroyed
each time the button
is clicked.
Form
Button1
Button2
Form--Module Code
Sub Button1_Click()
Dim i1 As Integer
i1 = 3
End Sub
Sub Button2_Click()
Dim i1 As Integer
i1 = 7
End Sub
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Programming: Global Variables
 Wider scope and lifetime
 Created at a higher level
 Form
 Public module
 Accessible to any procedure
in that form or module.
 Declare it Global to make it
available to any procedure.
Form
Button1
Button2
Form--Module Code
Dim i2 As Integer
Sub Button1_Click()
i2 = 20
End Sub
Variable is created when
form is opened.
Sub Button2_Click()
Clicking Button1 sets the
i2 = i2 + 7
initial value.
End Sub
Clicking Button2 modifies
the value.
What if user clicks buttons in a different order?
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Programming: Computations
 Standard Math
+ - * /
 \ Integer divide
 ^ Exponentiation
 (2^3 = 2*2*2 = 8)
 Mod
 (15 Mod 4 = 3) (12 + 3 = 15)
“Frank” & “Rose”  “FrankRose”
Left(“Jackson”,5)  “Jacks”
Trim(“
Maria “)  “Maria”
 String










& Concatenation
Left, Right, Mid
Trim, LTrim, RTrim
String
Chr, Asc
LCase, UCase
InStr
Len
StrComp
Format
Len(“Ramanujan”)  9
String(5,”a”)  “aaaaa”
InStr(“8764 Main”,” “)  5
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Programming: Standard Functions
 Numeric







x = loge (ex)
Exp, Log
Trigonometric
functions ?
Atn, Cos, Sin, Tan
=30
Sqr
92
2 = 1.414
Abs
Abs(-35)  35
Sgn
Sgn(-35)  -1
Int, Fix
Int(17.893)  17
Rnd, Randomize
Rnd()  0.198474
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Programming:
Standard Functions: Date/Time
 Date, Now, Time
 DateAdd, DateDiff




“y”, “m”, “q” . . .
Firstweekday
1=Sunday,. . .
Can also be used
to find number of
Fridays, between
two dates.
02/19/99
today
03/21/99
DateDue
DateDue = DateAdd(“d”, 30, Date())
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Programming:
Standard Functions: Variant
 Variant





IsDate
IsNumeric
VarType
IsEmpty
IsNull
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Programming: Debug






Stop
Ctrl-Break
F5: Go
F8: Step through
S-F8: Step over
Breakpoints
 Immediate Window
 ? or Print
 Any assignment
 Any code
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 MsgBox
Programming:
Output: Message Box
 Message
 Type
 Title
 Types: Use Constants




vbOKOnly vbOKCancel
vbAbortRetryIgnore
vbYesNoCancel
vbYesNo vbRetryCancel
 Defaults
 Icons




vbCritical Stop sign
vbQuestion Question mark
vbExclamation Warning
vbInformation Circle i
 Responses




vbOK
vbCancel
vbAbort vbRetry
vbIgnore
vbYes
vbNo
 vbDefaultButton1
 vbDefaultButton2
 vbDefaultButton3
MsgBox "This is a message box", vbYesNoCancel + vbInformation, "Sample Box"
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 InputBox




Programming:
Input: InputBox
Prompt
Title
Default
X-Pos, Y-Pos
 Prompt
 Cannot change box size
 Use Chr(10) & Chr(13) for
blank lines.
 Returns text or Variant
 Cancel = zero string ““
 Positions




Twips
Twentieth of inch point
72 points
1440 twips per inch
Dim str As String
str = InputBox(
"Enter your name:",
"Sample Input", ,
5000, 5000)
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Programming: Conditions
 If
 Conditions
 If (Condition) Then
 statements for true
 Else
 <, <=, >, >=, =, <>
 And, Or, Not, Xor
 Eqv, Imp (logic)
 statements for false
 End If
 IIF (Cond., True, False)
 Select Case (expr)
 Case value
 statements
 Case value2
 Case Else
 End Select
If (Condition1) Then
statements for true
Else
statements for false
If (Condition2) Then
statements for true
End If
End If
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Programming
Select Example
 Message Box
 Could use repeated If
statements
 Better to use Select Case
response = MsgBox(…)
If (response == vbYes) Then
‘ statements for Yes
Else
If (response == vbNo) Then
‘ statements for No
Else
‘statements for Cancel
End If
End If
response = MsgBox(…)
Select Case response
Case vbYes
‘ statements for Yes
Case vbNo
‘ statements for No
Case vbCancel
‘ statements for Cancel
End Case
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Programming: Loops
Initialize value
Statements
 Do
 For … Next
 For Each
Change value
Test condition
Do Until (x > 10)
Do While (x <= 10)
‘ Statements
‘ Statements
x=x+1
x=x+1
Loop
Loop
Do
For x = 1 to 10
‘ Statements
x=x+1
‘ Statements
Next x
Loop Until (x > 10)
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Programming: Loops Again
 Do
 For/Each (objects)
 Do {While | Until}
 Exit Do (optional)
 Loop
 For Each element In group
 [Exit For] (optional)
 Next element
 With (objects)
 Do
 Loop {While | Until}
 With object
 End With
 For/Next
 For counter = start To end
Step increment
 Exit For (optional)
 Next counter
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Programming
Subroutines and Functions
 Sub name (var1 As . . ., var2, . . .)
 End Sub
 Function fname (var1 As . . .) As datatype
 fname = …
‘ returns a specific value
 End Function
 Variables are passed by reference
 Changes made to the parameters in the subroutine are passed
back to the caller.
 Unless you use ByVal
 Changes are made to a copy of the parameter, but are not
returned to the calling program.
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Programming: Example Subroutine
Main program
…
StatusMessage “Trying to connect.”
…
StatusMessage “Verifying access.”
…
End main program
Sub StatusMessage (Msg As String)
‘ Display Msg, location, color
End Sub
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Programming: Parameter Types
Main
j=3
DoSum j
… ‘ j is now equal to 8
Subroutine DoSum (j2 As Integer)
j2 = 8
End Sub
Main
j=3
DoSum j
… ‘ j is still equal to 3
Subroutine DoSum (ByVal j2 As Integer)
j2 = 8
End Sub
By Reference
Changes to data in the
subroutine are passed back.
By Value
Creates a copy of the
variable, so changes are
not returned.
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Programming
Arrays and User Types

Arrays




Dim array(sub, . . .) As
type
Dim iSorts(10) As Integer




(lower To upper, . . .)
ReDim [Preserve] array ..
.
Option Base 0 | 1
v 2.0 arrays less than
64KB
Type Tname



Specifying bounds:

User defined types



ename1 As type
ename2 As type
End Type
Dim var1 As Tname
var1.ename1 = . . .
var1.ename2 = . . .
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Programming: Financial Functions

Fixed payments













PV (rate, nper, pmt, fv, due)
FV (rate, nper, pmt, pv, due)
IPmt (rate, per, nper, pv, fv,
due)
NPer (rate, pmt, pv, fv, due)
Pmt (rate, nper, pv, fv,due)
PPmt (rate, per, nper, pv, fv,
due)
Rate (nper, pmt, pv, fv, due,
guess)
rate
per
nper
pv
fv
due

Arrays




NPV (rate, array)
IRR (array, guess)
MIRR (array, finrate, re_rate)
Depreciation



DDB (cost, salv, life, period)
SLN (cost, salvage, life)
SYD (cost, salv., life, period)
interest rate per period
specific period number
# of periods
present value
future value
0=due at end, 1=due at start
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Programming: Text File Input/Output







Open filename As # file#
Close # file#, Reset
Print #,Put, Write
Spc, Tab
Get, Input #, Line Input #
EOF, LOF
Seek # file#, position





ChDir, ChDirve
Dir
Kill, (re)Name
Lock, Unlock
CurDir, MkDir, RmDir
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DDE: Dynamic Data Exchange




Shell
DDEInitiate
DDEExecute
DDEPoke, DDE Send




Application must be running
Start a conversation/topic
Issue a command
Place data
 Send data
 DDE, DDERequest
 Get data
 Request data
 DDETerminate
 Close the session
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OLE: Object Linking & Embedding
 CreateObject (class)
 “appname . objecttype”
 GetObject (file, class)
 Methods and syntax are
defined by the software that
exports the object.
 Example
 Dim obj As Object
 set obj =
CreateObject(“Word.Basic”)
 obj.Bold
 obj.Insert “text”
 obj.SaveAs “file”
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