1. CSI 101 Elements of Computing Spring 2009
Lecture #7 – Visual Basic Operations and Conditions
Monday, February 23rd, 2009 thru Wednesday, February 25th, 2009

2. Visual Basic Operations
How to get things done

3. Types of Operations Mathematical Operators Keywords Methods
Symbols that represent various mathematical operations
Keywords
Reserved words in the Visual Basic language
Perform specific actions
Methods
A specific function attached to an object

4. Mathematical Operations
Many calculations in Visual Basic are mathematical
Using a value contained in a variable, altering it somehow, and finishing with a result
Big difference between math and Visual Basic
The answer, or receiving variable, is ALWAYS to the left side of the equal sign
Example:
intCount = intCount + 1
This adds one to the value of variable intCount

5. Arithmetic Operators + - * / \ Mod ^ Note there is no symbol for roots
Addition
Subtraction
Multiplication
Division
Integer Division (has no decimal/remainder)
Modular division (returns remainder only)
Exponentiation

6. Arithmetic Examples
GPA = sumGrades / totHours dblAve = (int1 + int2 + int3) / 3 Sqr = intVal ^ 2 intDiff = A – B intRank = Total \ num 5 /4 is \ 4 is 1 6 MOD 4 is 2

7. Order of Operations Uses same order as math: Parentheses (inside out)
Exponentiation
Multiplication or division (left to right)
This includes integer division and modular division
Addition and subtraction (left to right)

8. Comparison Operators Less than < Greater than > Equal to =
Less than or equal to
Greater than or equal to
Not equal to
Joins two conditions: True if BOTH conditions are true
Negates current condition result
Joins two conditions True if AT LEAST ONE of the conditions are true
Joins two conditions: True if ONLY ONE of them is True
<
> =
<=
>=
<>
AND
NOT OR
XOR

9. Comparison Examples
intCount < 10 intSum > 200 AND intSum < 400 (Note that 200 < intSum < 400 is NOT known to Visual Basic) boolCheck = True OR Length < 10

10. Special Operators & += -= *= /= &= Concatenate strings Increment
Decrement
Multiplication assignment
Division assignment
Add string to end

11. Special Operator Examples
Start with intSample = 1
intSample += 2 sets intSample to 3
intSample -= 1 sets intSample to 2
intSample *= 3 sets intSample to 6
intSample /= 2 sets intSample to 3

12. Concatenation Examples
txtA = “Test A”, txtB =“BB”, txtC = “C”
txtC = txtA & txtB leaves A and B unchanged, txtC now is “TestABB”
txtA &= txtB leaves B unchanged, txtA now has “Test ABB”
txtC = txtA & “ “ & txtC leaves A unchanged, txtC now has “TestABB TestABB”

13. Conversion Operations
How to change things

14. Why use conversion?
Sometimes you have data of one data type (like string) and need to use it in a calculation as another type (like integer)
Does not alter the variable, since it was declared as a particular type
Allows the program to copy that value to a new variable of the desired data type

15. Convert from String Use the Parse method of a data type
For instance, to change to Integer, use the Integer.Parse( ) method
intValue = Integer.Parse(strValue)
The following data types have Parse methods:
Integer, Short, Long
Decimal, Single, Double
The following data types do not have Parse methods:
Boolean
Date

16. Convert To String All numeric types have a ToString method
txtTest = intCount.ToString( )
Boolean variables do NOT have a ToString method

17. Formatting Options
You can specify how you want the converted text value to look
Specify option within parentheses of ToString method

18. Numeric Formats Currency Fixed Number Digits Percent
Two decimal places, dollar sign preceding value, negative values enclosed in parentheses
Variable decimal places, no comma separators, negative sign preceding negative values
Fixed with comma separators
Number with no decimals
Multiplies value by 100, adds percent sign to end

19. Numeric Format Options
C or c
Fn or fn
Nn or nn
Dn or dn
Pn or pn
Currency
Fixed with n decimal places
Example: F3 has 3 decimal places
If no digit specified, uses two decimal places
Number with n decimal places
Digits of n digits long
Percent with n decimal places

20. Numeric Format Examples
intA = 12 and decA = 6.45
decA.ToString(“C”) yields $6.45
decA.ToString(“F3”) yields 6.450
decA.ToString(“N”) yields 6.45
decA.ToString(“N1”) yields 6.5
intA.ToString(“D3”) yields 012
intA.ToString(“P”) yields %
intA.ToString(“P0”) yields 12 %
Note that it rounds up if necessary

21. Condition Statements IF
How to decide what to do

22. Decision statements Select one action or another
Similar to the diamond-shaped box in flowcharts
Either True or False (Yes or No)
Condition evaluates to either True or False
Uses comparison operators
IF block contains condition(s)

23. IF statement forms Single-line: IF condition THEN action [ELSE action]
If condition is True, then perform action following the THEN keyword
The ELSE part is optional
If condition is False, action following ELSE is performed
Note that only one operation can follow the THEN or ELSE
Example: IF intCount < 10 THEN intCount += 1
Explain use of square brackets to denote optional

24. IF statement forms, cont
Multi-line:
Used if more than one operation is performed if condition is True or False
IF condition THEN
<actions>
ELSE
END IF

25. ELSEIF statement Provides a different condition
Performed if condition on IF was False
Inserted before ELSE
Now ELSE is run if BOTH conditions are False

26. ELSEIF format
IF condition THEN <actions> ELSEIF new_condition THEN ELSE END IF

27. IF Example
IF intCount < 10 THEN intSum += intNums(index) index += 1 intCount += 1 ELSE dblAve = intSum / 10 END IF

28. ElseIf Example
IF index< limit THEN intSum += intNums(index) index += 1 intCount += 1 ELSEIF dblAve = 0 THEN dblAve = intSum / intCount ELSE END IF

29. Nested IF
A multi-line IF block contained within another multi-line IF block
Used to process actions dependent upon two independent conditions

30. Nested IF Example Find smallest of three values: IF A < B Then
IF A < C Then Min = A Else Min = C
ELSE
IF B < C Then Min = B Else Min = C
END IF

31. Condition Statements SELECT
How to have lots to choose from

32. Select Case Statement Allows for multiple conditions
Conditions are values, not comparisons that result in True or False
Each condition can have multiple values
Will perform actions for first case that is found true
Never runs more than one, so whatever one is first wins

33. Select Case Format
Select Case expression Case values <actions> : [Case Else] [<actions>] End Select

34. Case Value lists Single value List of values Bounded values
Range of values
Case 5 TO 10

35. Select Case Example
Select Case intValue Case < 5 intValue += index index += 1 Case < 10 intValue += 2 Case < 20 intValue /= 2 End Select