1. Data Types, Arithmetic Operations
Lecture 2

2. What are we going to cover
Variables
Data types
Operators
Methods
Classes and objects

3. Variable 18
Address: 0803
Name: MyAge
Address: 0000
A variable is a symbolic name for a location in memory where some data are stored.
Every variable has its address in memory and value

4. Declaring variable in VB.NET
Dim n As Integer
Dim p As Double
Dim str As String
Dim weLikeFunPro As Boolean …
Name: n
0.0
Name: p
Name: str

5. Variable identifiers You can choose any name for variables as long as
the name is not already a word in the VB.NET language (such as class, imports);
the name has no spaces in it;
the name does not include operators such as “+” and “-”;
the name starts either with a letter or an underscore (_).
Valid names: correct, _correct
Invalid names: #wrong, ^wrong, 1wrong
Note: control names are variables, rules apply

6. Data Type
Every variable has its type identifying what sort of data should be stored in it:
Integer, String, Floating-point number etc.

7. Data Type It is very essential to show the type of the variable
Because internally the computer stores all the values in binary and does not differentiate the type.
The compiler needs to know the type in order to be able to convert the binary value into the specified type.
It also prevents logical errors e.g. if you try to assign some text into a numeric variable compiler would flag this as error.

8. Data Type
Integer: 70
Char: ‘ F ‘
Double: 70.0

9. Variable types (integer types)
VB.NET name
Description
Range
Byte
8-bit unsigned number
0 to 255
Short
16-bit signed number
to 32767
Integer
32-bit signed number
-2^31 to 2^31-1
Long
64-bit signed number
-2^63 to 2^63-1

10. Variable types (decimal types)
VB.NET name
Description
Precision
Range
Single
32-bit floating point number
7 significant digits
+/- 1.4x10^(-45) to +/- 3.4x10^38
Double
64-bit floating point number
15-16 significant digits
+/- 5.0x10^(-324) to +/- 1.7x10^308
Decimal
128-bit fixed point number
28 significant digits
+/- 1.0x10^(-28) to +/- 7.9x10^28

11. Variable types (other)
Char – one letter
String – text of any length
Date – date and time
Boolean – true or false

12. Conversion between types
Generally compiler should not let you to assign one data type to another
However in practice it uses implicit conversion for the types it knows how to convert e.g. Integer to Long
In VB.Net compiler is even more flexible allowing you to avoid some of explicit conversion required
Option Strict On will enable strict rules

13. Conversion between types
CType(value, class)
Dim a As Long = 1000
Dim b As Integer
b = CType(a, Integer)
CDbl
CInt

14. Conversion between types
All .NET languages – Convert class:
Convert.ToBoolean()
Convert.ToDateTime()
Convert.ToDecimal()
Convert.ToDouble()
Convert.ToInt32() - Integer
Convert.ToInt64() - Long

15. Assignment operation
Operator ‘=‘ represents the assignment operation which means: to assign the value of the expression on the right hand side of the ‘=‘ sign to the variable on the left hand side
n = 5
p = 2.6
Str = “Hello World”
weLikeFunPro = True 5
Name: n

16. Arithmetic operations
VB.Net supports all simple arithmetic operations:
+, - , *, /,
\ - integer division,
Mod – remainder division,
^ - exponentiation,
& - String concatenations

17. Arithmetic operations
P = (n * 3 + 2) mod 5
P = N / M
N = 5 ^ 3

18. Operator Precedence
Highest
Exponentiation (^)
* / \
Mod
+ -
Lowest

19. Constants
Constants are the variables whose values cannot be changed by the program
Declaring the constants:
Const PI As Single = 3.14
Const PASSWORD As String = “magic”

20. Comments
Comments are very useful tool that help the developers to put hints on the code blocks for future use.
Use single quote to point the comment string
‘ This is a comment line
Always use comments in your programs. This will make your life easier.

21. String functions
String class exposes a variety of methods to manipulate strings
String.Insert
String.ToLower, String.ToUpper
String.Substring
String.Split
String.Join
and many more…

22. Methods A method is a block of code. A method has a header and a body.
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
n = n + 1
p = p – 0.1
End Sub

23. Methods
Methods are used to break up the code from one monolithic peace into smaller reusable modules.
It is like breaking a big job into a smaller operations to be fulfilled by the different people
We will learn about functions and subroutines later

24. Classes and Objects
For now you can think of Classes as of Data Types and Objects as of Variables

25. Object properties and methods
Almost all objects have properties and methods.
To access to the object’s properties or methods use dot sign:
Label1.Text = “Hello World”
Objects can have a number of variables (properties), methods and other objects.

26. The Windows components
You can access the variables of the windows components at the design time using Properties Window
The methods and as well as properties of an object are also accessible in the code view:

27. The End