1. Visual Basic Numbers
Chapter 3.3
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7/9/2019

2. Topics to cover Arithmetic Operators Numeric Variables
Naming Conventions
Declaring Variables
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3. Arithmetic Operators * (Multiplication) / (Division) + (Addition)
- (Subtraction)
^ (Exponential)
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4. Expression Evaluation
In an expression in VB if No parentheses are used the equation is evaluated from left to right.
The order of operations is
Exponential
Multiplication & Division
Addition & Subtraction
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5. Calculations Additions + A + B Substraction - A – B Multiplication *
Division /
A / B
Exponentiation  ^
A ^ B
Left to Right
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6. Evaluate these equations
Assume
x = 2
y = 4
z = 3
X + Y ^ 2
8 / Y / X
X *(X + 1)
X * X + 1
Y ^ X + Z * 2
Y ^ (X + Z) * 2
(Y ^ X) + Z * 2
((Y ^ X) + Z) * 2
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7. ANSWERS 18 1 6 5 22 4 To Power of 5; multiply by 2 (2048) 38
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8. VB Data Types Boolean Byte Currency Date/time Double Integer Long
Single
String
Variant (default)
1) String or String Literal enclosed in quotes (literal) can be any characters, symbols, or numbers
example: strLastName = "Satzinger" strFirstName = "John" strFullName = strFirstName & strLastName
2) Integer a whole number (no decimal place) a numeric value, stored differently no quotes
example: intPageCounter = intAge = 29
3) Currency a number with decimal places used in calculations, not limited to "money" (no dollar sign)
examples: curSalesAmount = curSalesTax = curDiscountRate = .045
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9. Naming Conventions bln Boolean cur Currency dbl Double dtm Date int
Integer
lng
Long
sng
Single
str
String
vnt
Variant (default)
Just like objects have prefixes variable also have prefixes that we will use in this class. These will help you to identify different variable within the code and save you time during the debugging phase. Not using the correct prefix for objects and variables will costs you points in your home work and on test.
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10. VB Numbers
Numeric types in Visual Basic
Integer
Long
Currency
Single
Double
Variant
1 3
$3.00
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11. VB Data Types Memory Reqmts.
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12. Naming Rules and Conventions
Identifier Type Prefix
Identifier (name) 1 to 255 characters
Can use Letters, digits, underscores
Cannot use spaces, or reserved words
(Print, Name, Value, Sub, etc.)
strSocialSecurityNumber
curPayRate
intQuanity
lngPopulation
curTAX_RATE (constant)
Naming convention requires:
1) Identifier is meaningful -- A name that indicates the purpose
2) Begins with lowercase prefix specifying data type  
Starting with VB 6.0 the lowercase prefixes are now three letters as per the Microsoft MSDN Library
e.g., str  for string
int  for integer cur  for currency
For variables, capitalize each word of name after prefix
e.g.,          curHoursWorked
For constants, use full uppercase and underscore
e.g.,          curMINIMUM_WAGE
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13. When To Use a Numeric Data Type?
Only if data will be
used in a calculation, otherwise use String
Examples:
Course Number? Social Security Number? Room Number? Age?
Salary
Course Hours?
Pay rate
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14. Declaring Variables Implicit vs. Explicit
Option Explicit statement required in this class!!!!!
Dim statement (referring to Dimension or size)
This requires explicit declaration of variables.
You must declare all variables used in the program!
The Auto Fill In feature help you write your dimension statements.
If you find the Auto Fill In feature annoying it can be turn off by:
Tools/Options/Editor
Deselect the Auto List Members
Dim strCustomerName as String Dim intTotalSold as Integer Dim curDailySales as Currency
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15. Where to declare identifiers?
Identifier-another name for variable. (A variable is a data element that is part of a data file or used in calculations with the code section of your project).
Variables can be declared in the programs general declaration area or in procedures.
Variable declared in the GD area can be used in all procedures within the Form
Variables declared in Sub Procedures can only be used within that procedure. (Scope)
Scope or Focus
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16. Scope of Variables Visibility of Variable
Can it be seen or used in this location?
Global - used anywhere in project
Public - used to declare global variables
Module-Level Variables – used in all procedures of a form
mstrFirstName (module-level string)
Local – used only in the current procedure
Static – used only in a procedure but retains its value while form is executing
Need to control when and where a variable can be used or its value changed
Global Variable (In a later chapter)
Public Variable can be "seen" or used anywhere in the project (multiple forms)--Public rather than Dim
Module-Level Variable or sometimes-called Form-Level Variable, are variable that can be "seen" or used anywhere in the code attached to a form. They are declared in the General Declarations of the Form.
Local Variable—can be "seen" or used only in the procedure where it is declared and is Declared in the Procedure where it is used
You can indicate scope in the variable name for module variable by add a m to the variable name
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17. curTaxes = curTaxRate * curPay
Guidelines
Declare identifiers for Numeric values that will be needed in your program
If you need to use a literal value declare a constant in the GD
In the GD area declare constant values like this
Const sngTaxRate as Single = .76
Constant variable values may not be reassigned at run time. They hold the original value while the form is active.
We use variables to make our programs more functional. Using literals and numeric assignment of literal values within your programs causes the program to be hard to maintain. I call these magic numbers
Numeric Literals in programs require continual maintenance
Always declare a variable for your data and use that variable name in your calculation, and assignment statements. This will add to the lines of code needed but it will also make you program more functional
OK to assign numeric value to Label Caption
lblTotal.Caption = curSalesAmount + curSalesTax
HOWEVER: if the value will be used later for additional calculations it should be placed in a variable not a property. 
Basic Code Example
curTaxes = curTaxRate * curPay 
* Do not use numeric literals in calculations
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18. Calculations
Calculations can be preformed with variables, constants and with the properties of certain objects.
The Text property of a TextBox is actually a string. If you must use the data entered into the TextBox in a calculation you must use the Val Function to convert the text to a numeric value.
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19. Val Function curPrice = Val(txtPrice.Text)
Use Val function to convert String data to numeric data
curSalesAmount=Val(txtSalesAmount.Text)
Some programs declare all variables as string and use the val function to do calculations on numeric data.
The format is
curPrice = Val(txtPrice.Text)
Use for Validating data - (An additional process for validation will be used when the IF statement is introduced—“Is Numeric”)
if user types in number to text box, fine if user types anything else, Val returns 0 this prevents error conditions (like the non-numeric data error)
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20. Counting & Accumulation Sums
Declare Module-Level variables in the General Declaration section
mcurScoreSum mintTotalCount
In the TextBox procedure the basic code will look like this:
We use counter to count the number of time that a sequence of code has been executed.
We use accumulator variables to accumulate the value of data read into the program
Usually counters and accumulators are declared as modular or static variables
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21. Using The Format Function
To format means to control the way output will look, either on the screen or on a report.
VB 6 has four new formatting functions
FormatCurrency
FormatNumbers
FormatPercent
FormatDateTime
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22. Formatting Data
See Handout
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23. Format this numeric data
Your rate of pay (10.50) to 2 decimal places in curPayRate
The sales tax rate (.75) as a percentage in curSalesTax
With one decimal
With two decimals
The dtmTodaysDate to show a long date
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24. Answers FormatCurrency(curPayRate) $10.50 FormatPercent(curSalesTax)
FormatDateTime(dtmToday, vbShortDate)
$10.50
75%
75.0%
75.00%
9/7/00
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7/9/2019