VB Variables and Data 091200

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.

Types of data Variable Constant Literal

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

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.

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

2 General Variable Types Numeric NonNumeric

2 Basic types of Numeric Variables Integer Decimal

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

A relevant tangent…

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

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

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

Now that we have discussed integers we shall discuss decimal variables

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

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

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 0.0000144

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

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

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

NonNumeric Data Types

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

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

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

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

Remember all of this next part…

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.

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.

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

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)

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

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

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