Some computer fundamentals and jargon

Memory:

Basic element is a bit – value = 0 or 1

Collection of “n” bits is a “byte”

Collection of several bytes is a “word”

Byte

The smallest collection of bits that can hold a character. Usually 8 bits, but on some old or special computers may be 4 or fewer bits. We will assume 8 bit / byte Trivia: 4 bits in an 8 bit/byte world is called a “nibble”

Number of distinctly different characters that can be held in a byte: 256 00000000 through 11111111

Byte

Two major schemes (in the US anyhow) for encoding characters:

ASCII -- American Standard Code for Information Interchange

Originally designed for use with teletype machines and used only 128 characters.

Byte

Was limited, so extended two ways:

Extensions to ASCII --- define characters to occupy values 128 – 255. Not really standardized

EBCDIC (IBM)

Extended Binary Coded Decimal Interchange Code

Byte

Need to be aware of differences as same bit pattern gives different characters. Some computers / languages use ASCII, some use EBCDIC

0110 1111

ASCII: o (lowercase “O”)

EBCDIC: ? (Question mark)

The PC uses ASCII

Word

Word typically contains 4 bytes, but can be as few as two or as long as 8.

IBM used 4 bytes / word and this has become the standard.

Also standardized is the convention that the first bit represents the sign – 1 < 0, 0 >0

Word

0111 1111 1111 1111 = 32767

1111 1111 1111 1111 = -32768

But numbers come in two flavors:

Integers or whole numbers, as above

Real, or floating point, numbers

A 2 byte word

Word

Floating point numbers are scaled to fall between -1 and +1

Bits in the word are divided to represent the sign of the number, the exponent, and the sign of the exponent.

24505.0 0.24505 * 105

And gets translated as:

Word

0 000 0101 0 000 0011 1011 1101 0011 1010

Sign ofExponent( + )

Value of Exponent (5)

Sign ofNumber( + )

Value of number (245050)

The lead decimal point in 245050 is implied and taken care of by the computer

A couple of things to note:

1) The “numeric” part of a floating point number only has 27 bits, so is of limited precision (about 7 digits --- any thing else is garbage.

2) The exponent has 7 bits, so can range roughly from 2 –127 to 2 127 (10 -38 to 10 38 )

Why should you care????

When we start doing Visual Basic in Excel (VBA), will need to define the type of variable we are using. VBA recognizes several types:

Byte A single byte (8 bits) of dataString A sequence of bytes containing charactersInt 2 byte integerLong 4 byte integerSingle 4 byte real numberDouble 8 byte real number

Real (or floating point) numbers can be entered in a variety of ways

With the decimal point: 1234.0

With the power of 10 (formula): =1.234*10^3

With the “E” notation(Scientific notation)

1.234e3

Characters & Stings

For Excel, anything that is not a number or a formula is a string. If want a set of digits as a string, need to enclose in quote or quotation marks.

For VBA, need to define variables that will hold strings as string data types

As you might expect, both Excel and VBA have functions to convert strings to numbers and numbers to strings. But use with care.

Some programming concepts

Computers are dumb!

Will do only what you tell themWill do it very fastWill do it very accurately

A “program” is a set of very explicit instructions

Some programming concepts

A good analogy is developing a set of driving directions

Need to be accurateGo 2.5 miles and turn right on M 40

Need to be unambiguous (clear)Turn right just after the bank on the corner

Useful if can correct from errorIf reach the T intersection, you have gone too far

Some programming concepts

Programming languages have a variety of constructs from which to build the program

Assignment Statement: Variable = Variable or value

Logic statementBoolean Expressions: A > B, etc.If (Boolean Expression) then ……

Looping instructionsFor …. NextDo Until ….

Some programming concepts

Need to “Declare” variable types

In BASIC, declaration done as:

Dim var as Type

And can invoke functions and other prewritten modules

Print, read, sqrt,…..

A trivial example

Dim i as integerDim A as singleDim B as singleDim S as stringS = “Loop Done”A = 5.For i = 1 to 10

B = A*iif B > 20 then

B = A +iend if

Print BNext iPrint S

A trivial example

Would result in output that looks something like

5101520101112131415Loop Done

Programs usually broken into “modules”

Each module does one specific set of tasks e.g. Read / verify input data Perform specific operations

Prepare / print output

Modules --- two flavors

Subprograms --- do not return a value

Functions --- return a valuee.g. Sqrt(x)

Visual Basic

Is the language for programming in Word, Access,& Excel

Is the “Environment” in which the programming is done (called the Integrated Development Environment or IDE)

Visual Basic

Objects / Properties / Methods

Object

Property

Method

Noun

Adjective

Verb

Visual Basic

Range (“A3”).select

Range is an object

select is a method

(“A3”) is a modifier for the object

Note that object separated from method by a .

Activesheet.name

Activesheet is an object

name is a property

Visual Basic

The result is the name of the active sheet

Visual Basic

All objects have properties

Most objects have methods

Will work with only a few of the many objects, methods and properties

Will introduce them as needed

Visual Basic

Some of the objects

WorkbookWorksheetActiveSheetRangeFormChart

Note --- a “Cell” is not an object, but is a type of range object

Visual Basic

And to further confuse the issue objects can have objects as properties

And objects can be grouped into collections

Workbook = collection of worksheets

Visual Basic -- The Environment

From Excel --- toggle with alt F11

Notice 3 parts to the IDE

The Project areaThe Properties area

The blank (or work area)

We will use primarily the properties and work areas

Macros are a type of VBA module

“Recorded Macros” are exactly that A record of the key strokes

converted to VB code

Keyboard Macros

Quick way to develop a macro

Captures keystrokesAssigns a name & shortcut

Two places to store

Current workbookPersonal workbook

Current workbook

Macro only available in the workbook

Stays with the workbook

Personal workbook

Available to all workbooks you create in currentsession.

Does not travel with current workbook

Stored in a special area and needs to be opened.

Recorded keystrokes macros, if saved in current workbook, are VBA subprograms in the “modules” component of the IDE. Good way to look at how Excel is manipulated.

If saved in the Personal Workbook, will see the Personal Workbook available in the IDE Project window. Are in a module of the Personal workbook

Can record macros in two modes:

Absolute address mode – referenced cells are absolute addresses (i.e. $col$row)

Relative address mode – referenced cells are relative to the selected cell when the macro is recorded. That is, cell addresses may change each time macro is run.

We will use recorded macros primarily as a way to introduce VBA programming.

But you should be able to find a good use for them – great for repeated tasks.