Visual Basic .Net the Programming Language

1
Visual Basic .Net the Programming Language
Syntax and semantics
2
structure of computer languages

• data types (variables constants)
• assignment
• flow control
• - branching
• - looping
• input/output

3
Learning Objectives

• data types
• - variables and constants
• - scope lifetime
• - declaration (option explicit, option
  strict)
• assignment
• - numeric
• - string
• - date
• some useful functions controls
• - type conversion
• - date related (DateTimePicker)
• - numeric updown controls

4
Frequently-used data types

• integer
• short 2 bytes
  -32,768 to 32,767
• integer 4 bytes
  about /- 2 billion
• long 8 bytes a
  very large integer number
• real
• decimal 16 bytes 0 to
  28 digits of accuracy
• single 4 bytes 38
  to 45 digits of accuracy
• double 8 bytes 308
  to 324 digits of accuracy
• Boolean 2 bytes true
  or false
• string 2 bytes for each
  character up to 2 billion
• Unicode characters
• date 8 bytes
• object 4 bytes

5
Constants

• Named constants (programmer defined)
• e.g., const pie as single 3.1415
• Intrinsic constants (system provided)
• e.g., Color.White
• Color.Blue
• Color.Red
• Color.Yellow
• Color.Green
• ...

6
Structure of a VB Application
solution
Project (s)
A project embodies an application program.
Form(s)
Controls
7
Scope of variables constants
project Public (or friend) z as integer Public
(or friend) const k as integer 15
module (form) private y as integer private const
j as integer 5
local (sub)
dim i as integer const m as short 8
block (within a loop) For i 0 to 3 dim k as
integer Next i
8
Lifetime of Variables
- local, block procedure or block of code -
form-level when the form remains loaded -
project project
9
Declaration of Variables Constants

• option explicit on as default to enforce
• declaration
• Why is declaration a good idea?
• - e.g., dim monument as integer
• monument 345678
• .
• monumnet monument 75
• .
• local declaration
• - e.g., Private Sub command1_click()
• dim x as integer
• dim y
• const pie as single
  3.1415
• End sub

10
Declaration of Variables Constants

• form-level declaration
• where? Before the first procedure of a
  form
• e.g., private x, y, z as integer
• private const country as
  string The United States
• project-level declaration
• where? in a module
• e.g., public x as integer
• public const country The
  United States

11
Variable Declaration
12
Project-level Declaration
13
Structure of a VB Application
solution
14
Choose scope for variables
choose a scope as narrow as possible
15
Naming conventions

• prefix
• integer
• integer int
• long lng
• real
• decimal dec
• single sng
• double dbl
• Boolean bln
• string str
• date dat
  

Scope Prefix project
g module (form) m local
none
For example gstrCustomerName
16
Assignment (numeric)

• operators
• addition
• - subtraction
• multiplication
• / division
• exponentiation
• \ integer division
  5 \ 2 2
• mod modulus
  5 mod 2 1
• e.g., a (5 4) / 2

17
Assignment (string variable)

• empty string
• - e.g., dim x as string
• x
• text1.text x
• assign one string to another
• - e.g., text2.text text1.text
• string concatenation using
• - e.g., dim firstname, lastname as string
• firstname John
• lastname Smith
• label1.text firstname
  lastname
• concatenate with itself
• - e.g., dim name as string
• name Roberts
• name name Rogers

John Smith
18
Assignment (Date)

• e.g., dim date1, date2 as Date
• date2 3-6-98 215
• date2 March 6, 1998 215 pm
• date2 1415
• date1 1/20/97 with option
  strict off
• date1 212 am with
  option strict off

19
Option Strict

• Option Strict Off is the default setting.
• Change the setting by typing Option Strict On
  at the top of the code window.
• With Option Strict On, the system strictly
  enforces data type checking.

20
Option Strict

• With Option Strict Off, it is okay to write

Dim s as string, i as single s 34 i s / 2

• With Option Strict On, the code above will
  generate an error message

Option Strict On disallows implicit conversion
from string to single.
21
Widening narrowing
Dim i as integer Dim j as long i 35 j i
Widening store a variable value into another
variable with greater precision or
magnitude Narrowing the reverse
widening
22
Narrowing (Option Strict Off)
Dim i As Integer 4-bytes Dim j As Long
8-bytes j 3000000000 i j
The above code will generate a runtime exception,
but not a warning in design time.
23
data type conversion functions
Convert its argument to
Function
Dim x as integer Dim s as string x 5 s CStr(x)
CStr string CInt
integer CLng
long CSng single CDbl
double CDec
decimal CDate date
s 5
Dim d as date Dim s as string s 01/15/2003 d
CDate(s)
d 01/15/2002
24
DateTimePicker Control

• Important properties
• Format long, short, time
• Value date time selected or set
• MinDate, MaxDate

Label1.Text CStr(Month(DateTimePicker1.Value))
25
Date related Properties functions

• Now
• Today
• TimeofDay
• Year()
• Month()
• Day()
• Hour()
• Minute()
• Second()

26
The DateDiff function
datediff(interval, date1, date2) where interval
DateInterval.Day
DateInterval.Month
DateInterval.Hour e.g.,
datediff (DateInterval.Day, 1/16/97,
1/1/2006) 2541
27
Numeric UpDown Controls
28
Numeric UpDown Controls

• Important properties
• Minimum, Maximum
• Increment
• DecimalPlaces
• Value

29
Private Sub ComputeButton_Click() Handles
ComputeButton.Click Dim rate, period,
principal As Double Dim monthlypayment As
Double rate CDbl(UpDown1.Value / 12)
'convert to monthly rate period
CDbl(UpDown3.Value) principal
CDbl(UpDown2.Value 1000)
monthlypayment Pmt(rate, period, principal)
-1 lblResult.Text FormatCurrency(monthly
payment.ToString) lblResult.Visible
True End Sub
30
Private Sub ClearButton_Click() Handles
ClearButton.Click UpDown1.Value 0
UpDown2.Value 0 UpDown3.Value 0
lblResult.Visible False End Sub