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Tuesday, June 23, 2015
ALARM MESSAGE, EX1040 Lubrication Unit Alarm
Understanding Keywords and Syntaxes of VB.NET
Visual basic.net keywords and syntaxes were similar with the
previous version of visual basic. There are two terms in object oriented
programming, including visual basic.net:
1. Method: generic
name for command in visual basic. The Sub and Function are types of Method.
2. Instance: When a
class created, the object created was the instance from the class definition.
There are some keywords and descriptions you need to understand while programming on
OOP:
Keywords
|
Descriptions
|
Namespace
|
Classes collection that provides related ablities, for
example System.Drawing contains classes related with graphic.
|
Class
|
Definition of object, including properties (variable) and
method that can be a Sub or a Function.
|
Sub
|
Method that contains commands, enable data transferred as parameter
and provide scope inside local variable, but doesn’t return value.
|
Function
|
Method that contains commands, enable data transfered as parameter
and provide scope inside local variables and commands.
|
Return
|
Terminate Sub or Function currently executed. Can be
combined with return value for function.
|
Dim
|
Declare and define new variable
|
New
|
Create new instance from object.
|
Nothing
|
To indicate that a variable has no value. Similar with null
in other proramming languages, or in database.
|
Me
|
Reference to object inside the scope where the method
executed.
|
Console
|
Application type that run on command line. Console app in
dot net usualy needed for testing purpose only. Console also referes to class
that manage command window and can read and write text data.
|
Module
|
Block of codes but not a class, can contain Sub or Function
method. Used when there are only one code or data needed in the memory.
|
2.1 Compiler
Options
Before you type codes, you need to set compiler options.
There are many compiler options setup you can choose:
·
Option Explicit: This option don’t change from previous
version of visual basic. If it’s activated or enabled. It will make sure that
variabel declared explicitly. If you use Option Strict, this setting won’t be
problem, because compiler don’t recognize the type of the undeclared variables.
Basically, you dont have to use Option Explicit, unless you build a pure
dynamic solution, where compilation time for typing unavailable.
·
Option Strict: When this option enabled, compiler will
decide type of each variable. And if assignment between two variables need type
conversion, eg: from integer to boolean, this conversion should be expressed
explicitly.
·
Option Compare: This option make sure whether string has
to be compared as string binary, or character has to be compared as text. Text
comparation needs system to compare binary value saved internally before
compared.
·
Option Infer: This option exists since VS 2008 and added
because of LINQ requirement. When you execute LINQ statement, you will return
data table that can’t be typed in statement Advanced.
2.2 Variable
Variable
in programming language is a place to store information in computer memories.
You can imagine a variable like an empty box, you can save some value in
variable.
To add two
numbers for example, you just write first number on an empty paper and put the
paper on the empty box, then you write second number on an empty paper and put
the second paper on the empty box.
In visual
basic.net, this will be identical to this:
Dim number1 As Integer
Dim number2 As Integer
number1 = 3
number2 = 5
Codes
above are codes in visual basic.net that describe how Visual
Basic Net create and define variables.
Below are
the explanations on several keywords used while defining variables:
Dim
Dim stands
for “Dimension”. This keyword used to
declare variable type. By using this keyword, you are declaring a variable in
visual basic.
number1
This can
be compared with an emtpy box, label and it’s content. This is variable.
In other words, this is your storage area, the place where you save
your value.
After the
DIM, visual basic will name your variable. You can name the variable with everything you
like. But there are some reserved words you may not use.
As Integer
This
keywod describe the variabel type. Here, you tell visual basic that the
variable will be an integer. This will define the box’s size, different type
will make the size of the variable different.
number1 = 3
The “=”
character means you insert something to your variable. Here, you tell visual basic to set 3 to variable
number1.
2.3 Variable Types
Variable
has many types. In VB.net, each variabel type will have it’s own scope. And can consume spaces
in computer memory.
Boolean
Boolean variable can contain True and False data. Inside the visual baisc, the value saved as number 1
and 0 it represent True and False.
Boolean
value used as a conditional statement to determine whether some parts of the
codes will be executed or not. It’s for controlling the flow of the program.
Char
Char value contains one character, eg: “B”. Char value can be any
characters. It
can span from 0 to 65.553. It can also used to save data from ASCII table. Eg: Z can be used on char variable, and number 90 used in variable
location.
Byte
Byte variable contains positive number from 0 to 255. Because the range is very small, you
have to use byte variable wisely, if this variable inserted with negative value, or
value bigger than 255, this will cause an error.
Date
Date in visual basic can save date and time. Date should be inserted on
#mm/dd/yyyy#
format. For
example May 23, 2016 will be declared as #5/23/2016#.
Visual basic use some mechanisms to work with Date variable. For example to count six
months after today.
Decimal
Decimal
variable can save up to 29 decimal places. If you use decimal number, it’s okay
using this variable. If you use non decimal number, then use integer.
Double
Double variable used to save value that needs up to 28 decimal places. Double can be positive
values from range 4.94065645841246544E-324 to 1.79769313486231570E+308
negative values from -1.79769313486231570E+30 to
-4.94065645841246544E-324.
Double
variable usually used to develop a scientific application and rarely used by
regular developer.
Integer
Integer
variable used to save number between -2,147,483,648 until 2,147,483,648. This integer variable can’t save values that has
fractional value/decimal. If the value has fraction, it will be rounded
automatically.
Object
Object variable is a variable type that can be used to
save all types of data. Because of this flexibility, object variable consume
more memory space than other variable types. It’s not recommended to be used.
Use specific type that you need.
Long
Long variable used to save all numbers ranged from -9,233,372,036,854,775,808 to 9,233,372,036,854,775,807.
Short
Short
variable save number ranged from -32,768 to 32,767.
String
String
variable save characters that can construct word or statements. String variable
always opened and closed with quotation marks (").
For example "Hellow" or "Hellow, how
are you?".
Visual basic provides mechanisms to work with and manipulate
strings. Table below details variables that hold number data type. :
Name in VB
|
Size
|
Range
|
SByte
|
8 bits (1 byte)
|
-128 to 127
|
Byte
|
8 bits (1 byte)
|
0 to 255
|
Short
|
16 bits (2 bytes)
|
-32,768 to 32,767
|
UShort
|
16 bits (2 bytes)
|
0 to 65,535
|
Integer
|
32 bits (4 bytes)
|
-2,147,483,648 to 2,147,483,647
|
UInteger
|
32 bits (4 bytes)
|
0 to 4,294,967,295
|
Long
|
64 bits (8 bytes)
|
-9,223,372,036,854,775,808
to 9,223,372,036,854,775,807
|
ULong
|
64 bits (8 bytes)
|
0 to 18,446,744,073,709,551,615
|
Variable
types for floating points:
Name in VB
|
Size
|
Precision
|
Range
|
Single
|
32 bit (4 bytes)
|
7 digits
|
1.5 x 10-45 to 3.4 x 1038
|
Double
|
64 bit (8 bytes)
|
15-16 digits
|
5.0 x 10-324 to 1.7 x 10308
|
Decimal
|
128 bit (16 bytes)
|
28-29 decimals
|
1.0 x 10-28 to
7.9 x 1028
|
Other
prediefined:
Name
in VB
|
Size (bit)
|
Range
|
Char
|
16 bit (2 bytes)
|
One
unicode symbol ranges 0 to 65,535.
|
Boolean
|
32 bit (4 bytes)
|
True or False
|
Object
|
32/64 bit (4/8 bytes)
|
Platform
dependent (reference to object).
|
Date
|
64 bit (8 bytes)
|
January 1, 0001 12:00:00
AM to December 31, 9999 11:59:59 PM
|
String
|
80 + [16 * length] bit (10 + [2 * length] byte)
|
Unicode
strings with 2,147,483,647 characters maximum length.
|
To
allocate a numeric value, you can use equal sign “=”. To allocate a certain numeric value to variable
already declared, yo could use variable = certain_value.
For string and char variables, you can use quotation mark:
MystrVariable= "Some strings"
cMyhrVariable= "À"
For
date/time, you
can use hash/pound between value, by using this format #<month>/<day>/<year> <hour>:<minute>:<second> #.
For example:
MyDateVariable= #7/4/2016 12:01:50 PM#
For other
types, you don’t have to use anything.
myBytVariable = 1
mysbytVariable = -2
MyshrtVariable = 10S
MyushrtVariable = 10US
MyintVariable = 100
YouruIntVariable= 100UI
YourlnGVariable= 1000L
YouruLngVariable= 1000UL
sngVariable = 1.234F
dblVariable= 1.567R
decVariable = 1234567.89D
boolVariable = True
objctVariable = New Object
You can
also allocate value to variable on it’s declaration, for example:
Dim myVariable As String = "Another String Values"
Visual Basic will allocate value from right variable to the
left variable. Variabel in the left will take the value from the right variable. While the right
variable’s value won’t change.
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