More VB statements

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More VB statements

• Week 3

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Visual Basic Print Statement

• Print is a method used to display data on the
  screen or printer.
• Can be used to display values of variables or
  expressions

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For our F to C conversion program

• Draw a picture box and Name it picResult
• Draw a textbox and name it txtInput
• Draw your two command buttons
• In the procedure for Command button one
• Change the caption to C to F
• In the procedure put in
• picResult.Print (9/5) txtInput 32
• In the procedure for command button two
• Change the caption to F to C
• In the procedure put in
• picResult.Print (5/9) (txtInput 32)

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Program Documentation

• An apostrophe (') is used to indicate that the
  remainder of the line is a comment. (Comments are
  ignored by Visual Basic.)
• Remarks can appear on a separate line or
  following a Visual Basic statement.
• At the end of our Statement
• picResult.Print (9/5) txtInput 32
• We could have added a comment
• picResult.Print (9/5) txtInput 32 C to F

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Formatting the Output

• Create easily readable output
• In the Print method, the spacing of the output is
  controlled by the following devices
• semicolon
• comma
• Tab function

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Semicolons

• The next value output is placed in the next
  column position.
• Example
• picOutput.Print Lee Helen
• Output LeeHelen

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Semicolon

• Output statement that has added space in the
  second string
• picOutput.Print Lee Helen
• Output Screen Lee Helen

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Semicolon

• picOutput.Print 100 -200 300
• Output Screen
• 100 -200 300

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Commas

• A comma in a Print method that causes the next
  value output to be placed in the next available
  print zone.
• Each print zone is 14 positions wide.

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Using Commas

• Example
• picOutput.Print SEE, YOU, SOON
• Output Screen
• SEE YOU SOON

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Using Commas

• A print zone can be skipped by typing consecutive
  commas
• Example
• picOutput.Print HELEN, , LEE
• Output Screen
• HELEN LEE

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Tab Function

• Specifies the column where output will start
• Use only semicolons with the Tab function
• Can only be used to advance the print position
  (cannot move backwards)

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Example of Tab Function

• Example
• picOutput.Print Tab(3) Hello! Tab(22)
  Bye!
• Output Screen
• Hello! Bye!
• In the above example, the first Tab(3) causes the
  output to be placed in the 3rd space and the
  Tab(22) causes the output string to be placed in
  the 22 space.

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Assignment Statement

• The statement var expr assigns the value of the
  expression to the variable. (The variable must be
  on the left and the expression on the right.)
• ExamplePrivate Sub cmdCompute_Click( ) a
  4 b 3 (2 a)End Sub

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Valid Assignment Statements

• count count 1
• num 5
• count count num /2

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Invalid Assignment Statements

• 10 count
• count 1 count

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String Variables

• A string variable stores a string value.
• When a string variable is first declared, its
  value is a empty string.
• The rules for naming string variables are
  identical to those for naming numeric variables.
• Must begin with a letter 
• Must contain only letters, numeric digits, and und
  erscores ( _ ) 
• Can have up to 255 characters 
• Cannot be a Visual Basic language keyword 

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String Variable Example

• Private Sub cmdWords_Click()
• picOutput.Cls
• phrase it is not the grade that counts."
• picOutput.Print "It's learning VBasic " phrase
  
• picOutput.Print This is my wish" phrase
• End Sub

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Concatenation

• You can combine two strings by using the
  concatenation operation.
• The concatenation operator is the ampersand ()
  sign

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Examples of Concatenation

• strVar1 Hello
• strVar2 WorldPicOutput.Print strVar1
  strVar2
• txtBox.Text 32 Chr(176) Fahrenheit

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Declaring Variable Types

• Use the Dim statement to declare the type of a
  variable.
• Examples
• Dim number As Integer
• Dim flower As String
• Dim interestRate As Single

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Data Types

• Single a numeric variable that stores real
  numbers
• Integer a numeric variable that stores integer
  numbers (from -32768 to 32767)
• String a variable that stores a sequence of
  characters

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Using Text Boxes for Input/Output

• By default, the contents of a text box are always
  a string.
• Numbers can be stored in text boxes as strings.

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Using Text Boxes for Input/Output

• The contents of a text box should be converted
  to a number before being assigned to a numeric
  variable.
• Rememeber our little add program from the second
  week
• Val(txtBox.Text) gives the value of a numeric
  string as a number
• Example Dim numVar as Single numVar
  Val(txtBox.Text)

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Example (convert miles to furlongs and vice versa)

• Private Sub txtFurlong_LostFocus()
• txtMile.Text Str(Val(txtFurlong.Text / 8))
• End Sub
• Private Sub txtMile_LostFocus()
• txtFurlong.Text Str(8 Val(txtMile.Text))
• End Sub

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Files will be covered in lecture in around two
week

• Files are important to be able to setup record
  keeping systems.
• Today Ill introduce them in lecture since we
  need to assure that you understand the concepts.
• Will be very important for your class project.

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Steps in Reading Data from Files

• 1. Choose a number to be the reference number for
  the file
• 2. Execute an Open statement
• 3. Read the data sequentially using Input
  statements 4.
• Close the file

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Example of Reading from a File

• Open DATA.TXT For Input As 1
• Input 1, num1
• Input 1, num2
• Close 1

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Example of Reading from a File

• Open DATA.TXT For Input As 1 Input 1,
  num1, num2 picOutput.Print num1num2
• Close 1

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Tutorial

• Go to the on-line textbook and complete the two
  chapters
• Text boxes and buttons
• List, combos and forms.