1. VB Variables and Data
091200

2. About this Presentation
Do not feel you have to memorize all the technical details yet.
Know it well enough that you know you need to look it up when needed.
Know the basics.

3. Types of data
Variable
Constant
Literal

4. Variables
A variable is like a box in the computer memory for holding values.
Depending on the memory requirements of the variable, we may specify a large or small box. Dim intAge as Byte Dim curNationalDebt as Currency

5. A constant is a variable that doesn’t vary!
In other words, you may specify a value, such as PI, that you never want to change in your program.

6. Literal
A literal is a number that does not take up a variable position.
You simply refer to that number, such as 7 in this example: intHumanYears = intDogAge * 7

7. 2 General Variable Types
Numeric
NonNumeric

8. 2 Basic types of Numeric Variables
Integer
Decimal

9. Integer types Byte (0-255) 1 byte: 256 values
Integer (-32,768 to 32,767) 2 bytes: 256^2 values
Long (-2,147,483,648 to 2, 147,483,647) 4 bytes: 256^4 values

10. A relevant tangent…

11. A computer is really just a bunch of on/off switches
These switches, bits, come in sets of 8, called bytes

12. A single byte is 8 on/off switches containing 256 possible values:
0 1
0 2
0 4
0 8
0 16
0 32
0 64
0 128

13. The zeros represent OFF, the ones ON. This number is 49
1 1
0 2
0 4
0 8
1 16
1 32
0 64
0 128

14. Now that we have discussed integers we shall discuss decimal variables

15. Decimal types
Decimal types aren’t as simple as integer types, but still use bytes.

16. Decimal types Single 38 or more places 4 bytes
Double 308 or more places 8 bytes
Currency (-922 trillion to 922 trillion) 8 bytes

17. Scientific Notation
1.44E+5 = a number with the decimal shifted 5 places to the right: 144,000
1.44E-5 = a number preceded by 5 zeros

18. Forcing a Literal
Occasionally you may want to force a literal number to be more precise so the computer allocates enough memory for a calculated result.
& Long
! Single
# Double
@ Currency

19. For instance…
To add 7 to the curNationalDebt, you may refer to it as

20. Other Literals Date - Date Literal #September 1, 1964#
String - String Literal “Enclosed in Quotes”

21. NonNumeric Data Types

22. Nonnumeric Data Strings Text length+10 bytes Boolean True/False
2 bytes used
Date Various date formats 100AD to 9999AD
Variant All types of data
Numeric data uses 16 bytes String data uses Length + 22 bytes
Object The reference to an object

23. For this class, use variable prefixes:
Boolean blnYesOrNo
Byte bytAge
Currency curNationalDebt
Date dteBirthday
String strMyName
Variant vntUsesMemory continued

24. For this class, use variable prefixes:
Double dblKilometersToMars
Integer intStudentsAtMyHighSchool
Long lngUSPopulation
Object objMyStats
Single sngDistanceToMoon

25. How do you USE Variables…
Now that we have discussed them…
How do you USE Variables…

26. Remember all of this next part…

27. First, lets tell the computer to help us.
Add Option Explicit To the first line of your code, in the general declarations part of your code.
This catches misspelled variables that could cause you grief
It minimizes the chances of you using one name for two different intended variables.

28. Make your variable boxes, and make them the right sizes.
Dim bytAge as Byte
Dim datMyDOB as Date
Dim strMyName as String This is also done in general declarations, OR in a subroutine. If done in a subroutine it is used locally – in that subroutine only.

29. The variables are empty. You may now fill them as needed.
Let bytAge=36 or simply
bytAge=36

30. And you can do math… ^ Exponentiation bytYourAge=2^2
* Multiplication bytAge=9*4
/ Division byYourAge=24/3
+ Addition bytAge=30+6
- Subtraction bytAge=40-4 let bytAge=bytYourAge * 4.5
NOTE: Your book has errors in this (Table 5.5)

31. And more…
MOD Modulus intMyRemainder = 11 MOD 3 MOD only works with Integers.
\ Whole number division intMyWholePart = 11\3
intMyRemainder = 2, and intMyWholePart = 3
Because 11/3 is 3 remainder 2

32. Concatenation Concatenation means joining strings
We could use + or & but we won’t use the +
We will use "&" because it is easier to understand and distinguish from math

33. Math Operation Priority
Parentheses
Exponentiation
Multiplication, Division, Integer Div, MOD
Addition/Subtraction
Left to Right
Do some math examples!