1. CHAPTER FOUR VARIABLES AND CONSTANTS
COMPUTER MATHEMATICS
CHAPTER FOUR
VARIABLES AND CONSTANTS

2. USING NAMED CONSTANTS
Constant – memory location that stores a value that cannot be changed at run time from its initial value
Use constants for unchanging values to make program easier to read
Declared in a Const statement using identifier followed by the data type and an assignment

3. USING NAMED CONSTANTS Example: Const dblPi As Double = 3.14
This statement declares dblPi as data type Double and assigns the value of 3.14 to that memory location
Constants should be declared before variables at the beginning of a procedure
You cannot change the value of constant or an error will occur

4. CHOOSING IDENTIFIERS Must begin with a letter
Must contain only letters, digits, and the underscore (_) character
Periods, spaces and other special characters are not allowed
Cannot exceed 255 characters
Cannot use keywords reserved by Visual Basic such as ‘Double’

5. CHOOSING IDENTIFIERS Appendix A has a list of keywords
Name identifiers so that their meaning is clear
Prefixes describe the data type it will store
Descriptive names are important for later modification or debugging

6. LAB TIME
Review #3
Review #4

7. REVIEW #4 Examples: INPUT (reserved word) MY NAME (space)
23WESTCHESTER (begins with a number)

8. BUILT-IN DATA TYPES
Variable or constant be of the appropriate data type
Single – numbers possibly containing a decimal
Double - numbers possibly containing a decimal
Integer – integers (no decimals)
Long – integers (no decimals)
Currency – numbers representing dollar amount
String – a set of characters
Boolean – True or False

9. Single or Double Data Types
Positive or negative real numbers
Referred to as floating point
Difference between two types is the range of values it can store
Single - can store values up to 3.4e38
Double – can store values up to 1.8e308

10. Integer and Long Data Types
Positive or negative integers
No decimals
Difference between two types is the range of values it can store
Most times Integer is sufficient
Integer range – 32,767
Long range – anything greater than 32,767
If a decimal value is assigned to an integer variable the value is rounded

11. CURRENCY, STRING, BOOLEAN DATA TYPES
Currency – can store values with up to four digits to the right of the decimal place and 15 digits to the left of the decimal place
String – any set of characters enclosed in double quotation marks
Boolean – True or False values only; good for representing Yes/No; Heads/Tails

12. VARIABLE PREFIXES Single – sgl Double - dbl Integer – int Long – lng
Currency – cur
String – str
Boolean - bln

13. VARIABLE DECLARATIONS
A single Dim statement can be used to declare several variables
Example:
Dim strSchool As String, intGrade as Integer
Variables are initialized when declared; numeric values are zero, string variable blank (“”) and Boolean is False

14. OPTION EXPLICIT Can be added to the General section of the form module
Option Explicit displays error messages at run time when a variable is used before it is declared
Select General from the Object list in the Code Editor window
Type Option Explicit
To make the Option Explicit statement automatically appear chose Options command from Tools menu then the Require Variable Declaration option from the Editor Tab

15. CLASSWORK
Review #5

16. CLASSWORK ANSWER Dim strFirstName as String, strMiddleName as String
Dim strLastName as String, intAge as Integer
Dim dblGPA as Double

17. Vocabulary Quiz Chapter Four Pg. 4-24
HOMEWORK
Vocabulary Quiz
Chapter Four
Pg. 4-24