VB Variables and Data

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 ByteDim 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 places4 bytes • Double 308 or more places8 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 zeros0.0000144

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 7@

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

21. NonNumeric Data Types

22. Nonnumeric Data • Strings Textlength+10 bytes • Boolean True/False 2 bytes used • Date Various date formats100AD to 9999AD • Variant All types of data Numeric data uses 16 bytesString 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 vntUsesMemorycontinued

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…

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 StringThis 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=36or 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=40-4letbytAge=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 divisionintMyWholePart = 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!