csi 1306 programming in visual basic part 2. part 2 1. strings 2. translating conditional branch...

CSI 1306

PROGRAMMING IN VISUAL BASIC

PART 2

Part 2

1. Strings2. Translating Conditional Branch Instructions3. Translation Set 24. Debugging Programs5. Additional Material

1. Strings

Strings

A string is any combination of letters, numbers or symbols surrounded by double quotes " "

Two strings are considered equal if and only if each and every character is identical– “Bob” is equal to “Bob”

– but not equal to “BOB”, “bob” or “Robert”

Strings can be manipulated in assignment statements

Strings

The following operators can be used on Strings– Len, Lcase, Ucase, Right, Left, InStr, Ltrim, Rtrim,

Trim, Val, Str, &For example

– Str(Number)• converts a numeric type into a string• Str(456) “ 456”

– Concatenation (joining two strings) • done with & (ampersand)• “Hello” & “World” “HelloWorld” (no space)

These operators are defined in the Additional Material at the end of the lecture slides

2. Translating Conditional Branch Instructions

Review of Comparisons

The arithmetic logic unit in the central processing unit of a computer is capable of comparing 2 numbers

The result of the comparison is either a True or a False

We use the result to determine which block of code to execute (conditional branch) or whether to exit a loop


Comparisons can be made on both numeric and string data types

The comparison operators in Visual Basic are– < Less Than

– > Greater Than

– = Equal

– <= Less Than or Equal

– >= Greater Than or Equal

– <> Not Equal

Conditional Branch Instructions

IF statementIF (condition) THEN

instruction blockEND IF

Condition is a variable or expression which must evaluate to either True or False

If the condition is True, then execute the instruction block

If the condition is False, do not execute the instruction block


Write a program that will order the values of X and Y so that the smaller value will be in X and the larger value will be in Y.

Use the concept of a SWAP


OPTION EXPLICIT'Written by T. James

Sub swap ()Dim X as Single 'A ValueDim Y as Single 'A ValueDim Temp as Single 'Hold for a swap

If (X > Y) Thentemp = X X = YY = temp

End IfEnd Sub


Are the results identical when these two code fragments are executed?

IF (big > small) THEN big = smallEND IFsmall = 0

IF (big > small) THEN big = small small = 0END IF

In the left code fragment, small becomes zero only when big is greater than small.

In the right code fragment, small always becomes zero

Conditional Branch Instructions IF statement with an ELSE clause

What if we need multiple related tests?

IF (x > 5) THEN do instruction block 1END IFIF(x <= 5) THEN do instruction block 2END IF

IF (x > 5) THEN do instruction block 1ELSE do instruction block 2END IF


IF statement with ELSEIF clausesIF (condition 1) THEN

Do instruction block 1

ELSEIF (condition 2) THENDo instruction block 2

ELSEIF (condition 3) THEN Do instruction block 3

ELSEDo instruction block 4

END IFCan include any number of ELSEIF clausesThe ELSE clause may be omitted


ALGORITHMIf student is a Male

Let Mark = 60%Midterm + 40%Final

OtherwiseLet Mark = 40%Midterm + 60%Final

If Mark > 80Let Grade = A

Else If Mark > 60Let Grade = C

ElseLet Grade = F

VISUAL BASICIf (Gender = “M”) Then

NG = 0.6*MT + 0.4*FEElse

NG = 0.4*MT + 0.6*FEEnd If

If (Mark > 80) ThenGrade = “A”

ElseIf (Mark > 60) ThenGrade = “C”

ElseGrade = “F”

End If


Write an IF statement to assign the correct grade to an exam mark

– A if exam mark is 90 or above

– B if exam mark is 80 to 89

– C if exam mark is 70 to 79

– D if exam mark is 60 to 69

– F if exam mark is below 60

Conditional Branch InstructionsOPTION EXPLICIT'Written by T. James

Sub Grades ()Dim Mark as Single 'Final MarkDim Grade as String*1 'Letter Grade

If (Mark >= 90) ThenGrade = "A"

ElseIf (Mark >= 80) ThenGrade = "B"

ElseIf (Mark >= 70) ThenGrade = "C"

ElseIf (Mark >= 60) ThenGrade = "D"

ElseGrade = "F"

End IfEnd Sub


What is wrong with this code fragment?If (Mark >= 60) Then

Grade = “D”ElseIf (Mark >= 70) Then

Grade = “C”ElseIf (Mark >= 80) Then

Grade = “B”ElseIf (Mark >= 90) Then

Grade = “A”Else

Grade = “F”End If

The only two grades ever assigned are D and F


Note that in a comparison, if Pass is a Boolean variable

If (Pass = True) Then

is the same as

If Pass Then

and

If (Pass = False) Then

is the same as

If (not Pass) Then

Conditional Branch InstructionsFor choosing among integer values of a variable,

the SELECT CASE statement may be usedSELECT CASE variable

CASE value1Do instruction block 1

CASE value2Do instruction block 2

CASE ELSEDo instruction block 3

END SELECTCan include any number of CASE clausesThe CASE ELSE clause may be omitted


IF (X=1) THENY = 5

ELSEIF (X=3) THENY = 4

ELSEIF (X=6) THENY = 3

ELSEY = 2

END IF

SELECT CASE XCASE 1

Y = 5CASE 3

Y = 4CASE 6

Y = 3CASE ELSE

Y = 2

END SELECT

The two code fragments accomplish the same result. The one on the right is easier to read.


For choosing among multiple ranges of values of a variable, the CASE IS clause can be usedSELECT CASE variable

CASE IS range1Do instruction block 1

CASE IS range2Do instruction block 2

CASE ELSEDo instruction block 3

END SELECT


IF (X<10) THENY = 5

ELSEIF (X<20) THENY = 4

ELSEIF (X<30) THENY = 3

ELSEY = 2

END IF

SELECT CASE XCASE IS <10

Y = 5CASE IS <20

Y = 4CASE IS <30

Y = 3CASE ELSE

Y = 2

END SELECT

The two code fragments accomplish the same result

Translating Conditional Branch InstructionsLook at the METHODEach conditional branch instruction should be

translated to an IF (or, if appropriate, a SELECT CASE) statement

Make your code easy to read. Use a uniform indentation scheme

3. Translation Set 2

Translate 4

Translate Algorithm 2.4

Name: FAREGiven: Age

Change: NoneResult: PriceIntermediates: NoneDefinition: Price := FARE(Age)

Get AgeIf (Age < 16)

Let Price = $7Else If (Age > 65)

Let Price = $5Else

Let Price = $10Give Price

Translate 4






Let Price = $5Else


Option Explicit

'Written By T. James

Sub Fare()

Dim Age as Integer

Dim Price as Single

Age = InputBox("Age?")

MsgBox("Fare is " & Price)

End Sub

Translate 4






Let Price = $5Else


Option Explicit


Sub Fare()

Dim Age as Integer

Dim Price as Single

Age = InputBox("Age?")

MsgBox("Fare is " & Price)

End Sub

If (Age < 16) Then

Price = 7.00

ElseIf (Age > 65) Then

Price = 5.00

Else

Price = 10.00

End If

Algorithm 2.4

Translate 5

Translate Algorithm 2.2Name: BIG3Givens: N1, N2, N3Result: LargestIntermediate: NoneDefinition: Largest := BIG3(N1,N2,N3)

Get N1Get N2Get N3

If (N1 > N2)Let Largest = N1

Else Let Largest = N2

If (N3 > Largest)Let Largest = N3

Give Largest

Translate 5Translate Algorithm 2.2Name: BIG3Givens: N1, N2, N3Result: LargestIntermediate: NoneDefinition: Largest := BIG3(N1,N2,N3)

Get N1Get N2Get N3




Give Largest

Option Explicit


Sub Big3 ()

Dim N1 as Integer

Dim N2 as Integer

Dim N3 as Integer

Dim Largest as Integer

N1 = InputBox("N1?")



Translate 5 Translate Algorithm 2.2Name: BIG3Givens: N1, N2, N3Result: LargestIntermediate: NoneDefinition: Largest := BIG3(N1,N2,N3)

Get N1Get N2Get N3




Give Largest

Option Explicit'Written By T. JamesSub Big3 () Dim N1 as Integer Dim N2 as Integer Dim N3 as Integer Dim Largest as Integer N1 = InputBox("N1?") N2 = InputBox("N2?") N3 = InputBox("N3?")

If (N1>N2) Then Largest = N1 Else Largest = N2 End If

If (N3 > Largest) Then Largest = N3 End If

MsgBox("L = " & Largest)End Sub

Algorithm 2.2

Translate 6 Translate Algorithm 2.5Name: MEDICALGiven: Expense

Change: NoneResult: RefundIntermediates: LL, UL (Constants)Definition: Refund := MEDICAL(Expense)

Set LL = 100Set UL = 2,000Get Expense

If (Expense <= LL)Let Refund = 0

Else If (Expense <= UL)Let Refund = 90% (Expense-LL)

ElseLet Refund = 90% (UL-LL) +

100% (Expense - UL)Give Refund








Option Explicit


Sub Medical()

Dim Expense as Single

Dim Refund as Single

Const LL = 100

Const UL = 2000

Expense=InputBox("E?")








Option Explicit'Written By T. JamesSub Medical() Dim Expense as Single Dim Refund as Single Const LL = 100 Const UL = 2000

Expense=InputBox("E?")

If (Expense <= LL) Then

Refund = 0

ElseIf (Expense<=UL) Then

Refund = .90*(Expense-LL)

Else Refund = 0.9*(UL-LL)+Expense-2000

End If

MsgBox("Refund " & Refund)

End Sub

Algorithm 2.5

4. Debugging Programs

Debugging Programs

Step 1– Check the translation from your algorithm to Visual

Basic

Step 2– Recheck the logic in your algorithm

Step 3– Use the debug facilities of Visual Basic

Debugging Programs

To debug a program is to identify and correct errors in your program– Usually, these are semantic (logic) or runtime errors.

You will already have corrected most syntax errors when entering the code

Add Watch capability– Shows the current value of variables and expressions

as the program executes

Debugging Programs

Step Into your code– Runs the next executable line of code. If the code calls

another program, your view of the code shifts to the called program until it ends

– Step Over also runs the next executable line of code. However, if the code calls another program, the entire called program is run so that your view of the code is never shifted from the calling program

Using the watch and step into debug capabilities is analogous to tracing

Debugging Programs

For programs with many lines of code, where you might not want to step through each line of executable code, you can set breakpoints

Toggle Breakpoint– Creates or removes a breakpoint, a location in the code

where Visual Basic halts executionQuick Watch

– During break mode, lets you check the value of a variable or expression for which you have not defined a watch

4. Additional Material

String Operators

String Operators

Len(String)– returns the number of characters in the String– Len(“Hello World”) 11

Lcase(String)– changes all the characters in String to lower case– Lcase(“Hello World”) “hello world”

Ucase(String)– changes all the characters in String to upper case– Ucase(“Hello World”) “HELLO WORLD”

String Operators

Right (String, N)– returns the last N characters in the String– Right(“Hello World”, 5) “World”

Left (String, N)– returns the first N characters in the String– Left(“Hello World”, 5) “Hello”

InStr (String1, String2)– returns a number, counting from the left, where String2

can be found in String1 – returns 0 if String 2 is not in String1– InStr(“Hello World”, “World”) 7

String Operators

Ltrim (String)– eliminates leading blanks– Ltrim (“ Hello “) “Hello “

Rtrim(String)– eliminates trailing blanks– Rtrim (“ Hello “) “ Hello“

Trim(String)– eliminates both leading and trailing blanks– Trim (“ Hello “) “Hello“

String Operators

Val(String)– converts a string (consisting of numbers) into a numeric

type– Val(“123”) 123

Str(Number)– converts a numeric type into a string– Str(456) “ 456” (a leading space is always reserved

for the sign)Concatenation (joining two strings)

– done with & (ampersand)– “Hello” & “World” “HelloWorld” (no space)

Homework

For each of the following questions:Develop an algorithm

Translate the algorithm into Visual Basic Code

•Write an algorithm to reverse the digits in a three digit number and then add that number to 500. For example, 468 becomes 864. When added to 500, the result is 1364.

•Write an algorithm to get the names and ages of two people. Return the name of the person who is older (in the format “x is older than y”, where x and y are the names of the two people), unless the two people are the same age, in which case, return the message “x is the same age as y”.

An automotive sales representative’s commission is calculated as a percentage of the sale: – 8% of the first $5,000.00 of the sale price– 10% on the remainder of the sale price, if the remainder

is less than or equal to $80,000.00 or– 12.5% on the remainder, if the remainder is more than

$80,000.00Develop the visual basic code that will accept the

sale price of the automobile and calculate and display the sales representative’s commission.

csi 1306 programming in visual basic part 2. part 2 1. strings 2. translating conditional branch...

Documents