Visual Basic Statements

Relational Operators

• Equal =

• Less than <

• Greater than >

• Not equal <>

• Less than or equal <=

• Greater than or equal >=

Logical Expressions

Let A = x^2 -50 & B = x *(x – 70)• A < B

– True if A is less than B– False if A is not less than B

• A > B• A <> B

– True if A is not equal to B– False if A is equal to B

• A <= B; A >= B; A = B

Logical Expressions

• String comparisonsFirstName = ”Allama”

SecondName = “Muhammad”

LastName = “Iqbal”

– Equality• If FirstName=LastName Then…• If LastName <> SecondName Then...

– Inequality (Alphabetic ordering)AFlag = FirstName > Last Name

» Same as AFlag = True

Logical Expressions

• String comparisons– Less than Comes before– Greater than Comes after

• Uppercase precedes lower case• Blank spaces precede nonblank characters• Shorter string precedes longer string

» Car precedes Cart

Logical Operators

• Not This Not

• This And That And

• This, That Or Both Or

• Either This or That Xor

• A Equivalent to B Eqv

• A Implies B Imp

Not

A Not A

True False

False True

X=3Y=5

W = X > YZ = Not X>Y

W = FalseZ = True

And

A B A And B

False False False

False True False

True False False

True True True

(X > 10) And (X < 20)is True only when

10 < X <20

Or

A B A Or B

False False False

False True True

True False True

True True True

(X > 10) Or (X < 20)will always be True

(X < 10) Or (X > 20)will be False when

10 ≤ X ≤ 20

Xor (Exclusive Or)

A B A Xor B

False False False

False True True

True False True

True True False

(X > 10) Xor (X < 20)will be False only when

11 ≤ X ≤ 19

(X < 10) Xor (X > 20)will be False when

10 ≤ X ≤ 20

Equivalent

A B A Eqv B

False False True

False True False

True False False

True True True

Implies

A B A Imp B

False False True

False True True

True False False

True True True

If…Then…End If

If expression ThenStatement(s)

End If

Expression

Statement(s)

True

False

If…Then…Else…End If

If expression ThenStatement(s) I

ElseStatement(s) II

End If

Expression

Statement(s) I

TrueFalse

Statement(s) II

Solution of Quadratic Equation

Private Sub Command1_Click()Dim A As Integer, B As Integer, C As IntegerDim D As Single, X As Single, Y As SingleDim Ans1 As String, Ans2 As StringDim X1 As Single, X2 As Single‘ Read Coefficients of the quadratic equationA = Val(Text1.Text) 'Coefficient of x^2B = Val(Text2.Text) 'Coefficient of xC = Val(Text3.Text) 'Constant‘ Evaluate Discriminant as DD = B ^ 2 - 4 * A * C

Solution of Quadratic EquationIf D >= 0 Then' Roots are real. Equal or unequal X1 = ( -B + Sqr(D) ) / (2 * A) X2 = ( -B - Sqr(D) ) / (2 * A) Ans1 = Str(X1) Ans2 = Str(X2)Else' Roots are complex. Just need the absolute value

of the imag. part X =Abs( Sqr(Abs(D)) / (2 * A)) Y = -B / (2 * A) Ans1 = Str(Y) & " + i " & Str(X) Ans2 = Str(Y) & " - i " & Str(X)End If

Solution of Quadratic Equation

Text4.Text = Ans1Text5.Text = Ans2End Sub

• Assuming that 5 text boxes are created.

• Text1Text3 are used to input A, B & C

• Text4 & Text5 are used to display answers

If…Then…Else If…Else…End IfIf expressionA Then

Statement set A

Else If expressionB

Statement Set B

Else If expressionC Then

.

.Else

Statement Set N

End If

If…Then…Else If…Else…End If

Expression A

Statement Set A

Expression B

Statement Set B

Expression k

Statement Set k

True True

False False

Statement Set N

TrueFalse

Use of If…Then…Else If…

D = B ^ 2 - 4 * A * CIf D < 0 Then Message = "Roots are complex"ElseIf D = 0 Then Message = "Roots are real & repeated"ElseIf D > 0 Then Message = "Roots are real & distinct"End If

Select Case

Select Case expression

Case value set 1

Statement Set 1

Case value set 2

.

.Case Else

Statement Set N

End Select

List separated by commas Values; 1, 3, 5 String(s); “a”, “5”Range using ToNumbers; 6 To 8String; “A” To “Z” , “0” To “9”Logical expression using IsNumbers: Is >= 9String: Is < “h”

Not necessary

Using Select CaseD = B ^ 2 - 4 * A * Cn = Sgn(D)Select Case nCase -1 Message = "Complex roots"Case 0 Message = "Real repeated roots"Case 1 Message = "Real distinct roots"End Select

Using Select Case

D = B ^ 2 - 4 * A * CSelect Case DCase Is < 0 Message = "Complex roots"Case Is = 0 Message = "Real repeated roots"Case Is > 0 Message = "Real distinct roots"End Select

Using Select CaseDim Character As StringSelect Case CharacterCase "A" To "Z", "a" To "z" Message = "Character is Alphabet"Case "0" To "9" Message = "Character is Numeric"Case Else Message = "Character is not Alphanumeric"

End Select

Format Library function

Y = Format(x, “formatstring”)• Returns the value of x in a format designated by

“formatstring”

– Some built-in format functions• Standard• Currency• Percent• Scientific• Long Date• Medium Date

Format Examples

Y = Format(1450.0365, “Standard”)

Y = “1,450.04”

Y = Format(1450.0365, “Currency”)

Y = “$1,450.04”

Y = Format(0.03657, “Percent”)

Y = “3.66%”

Y = Format(1450.0365, “Scientific”)

Y = “1.45E+03”

Format Examples

Y = Format(Now, “Long Date”)

Y = “Wednesday, October 1, 2003”

Y = Format(Now, “Medium Date”)

Y = “01-Oct-03”

Y = Format(Now, “hh:mm:ss am/pm”)

Y = “09:07:23 am”

Format Examples

Y = Format(“CS101”, “@@@@@@@@”)

Y = “bbbCS101”

b stands for blank. Or CS101 is right-justified.

Y = Format(“CS101”, “&&&&&&&&”)Y = “CS101” Right blanks are truncated

b stands for blank. Or CS101 is left-justified.

CS101CS101

File Handling

• Files are used for large data input/output

• Create a .txt file called CarData by using Notepad (or ASCII file using other software) with following contents

“Suzuki”, 3, 4

“Toyota”, 5, 7

“Honda”, 4, 15

File Handling

• Files must be Opened before any read/write operation.

• Files must be Closed after any read/write operation

• SyntaxOpen “CarData” For Input As #138

» Opens a file called CarData.txt for read-only and this file will be called #138

» The file reference number can be from 1 to 255

File Handling

Input #138, Make, NoOfModels, NoOfColors » Assumes that the 1st line of “CarData.txt” contains 3

values corresponding to the three variables.» Make should be a string variable, while NoOfModels

and NoOfColors is a numeric type (Integer etc)

• After this Input statement» Make = “Suzuki”» NoOfModels = 3» NoOfColors = 4

Close #138

File Handling

Dim Make As String, NoOfModels As IntegerDim NoOfColors As IntegerOpen "C:\CarData.txt" For Input As #1Input #1, Make, NoOfModels, NoOfColorsOpen "C:\DataOut.txt" For Output As #2Write #2, Make, NoOfColors, NoOfModelsInput #1, Make, NoOfModels, NoOfColorsWrite #2, Make, NoOfColors, NoOfModelsInput #1, Make, NoOfModels, NoOfColorsWrite #2, Make, NoOfColors, NoOfModelsClose #1Close #2

File Handling

"Suzuki", 3, 4

"Toyota", 5, 7

"Honda", 4, 12

"Suzuki",4,3

"Toyota",7,5

"Honda",12,4

Contents of CarData.txt

Contents of DataOut.txt

File HandlingDim Make As String, NoOfModels As IntegerDim NoOfColors As Integer, FMake As StringOpen "c:\CarData.txt" For Input As #1Open "c:\DataOut.txt" For Output As #2Input #1, Make, NoOfModels, NoOfColorsFMake = Format(Make, "@@@@@@@@")Write #2, FMake, NoOfColors, NoOfModelsInput #1, Make, NoOfModels, NoOfColorsFMake = Format(Make, "@@@@@@@@")Write #2, FMake, NoOfColors, NoOfModelsInput #1, Make, NoOfModels, NoOfColorsFMake = Format(Make, "@@@@@@@@")Write #2, FMake, NoOfColors, NoOfModelsClose #1Close #2

File Handling

"Suzuki", 3, 4"Toyota", 5, 7"Honda", 4, 12

" Suzuki",4,3" Toyota",7,5" Honda",12,4

Contents of CarData.txt

Contents of DataOut.txt

File HandlingDim Make As String, NoOfModels As IntegerDim NoOfColors As Integer, FMake As StringOpen "c:\CarData.txt" For Input As #1Open "c:\DataOut.txt" For Output As #2Input #1, Make, NoOfModels, NoOfColorsFMake = Format(Make, "@@@@@@@@")Write #2, FMake, NoOfColors, NoOfModelsInput #1, Make, NoOfModels, NoOfColorsFMake = Format(Make, "&&&&&&&&")Write #2, FMake, NoOfColors, NoOfModelsInput #1, Make, NoOfModels, NoOfColorsFMake = Format(Make, "@@@@@@@@")Write #2, FMake, NoOfColors, NoOfModelsClose #1Close #2

File Handling

"Suzuki", 3, 4"Toyota", 5, 7"Honda", 4, 12

" Suzuki",4,3"Toyota",7,5" Honda",12,4

Contents of CarData.txt

Contents of DataOut.txt