Input and Output

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Input and Output

• Reading Data From Files
• Data files can be created with Windows NotePad,
  MSWord, or any another text editor. It is
  important to save the files as an text only,or
  text only with line breaks.
• A file can have either one item per line or
  many items (separated by commas) can be listed on
  the same line.
• Example the following file contains payroll
  information. Each line contains the name of a
  person, that persons hourly wage, and the number
  of ours that person worked during the week.

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• ______________________________________
• Mike Jones, 7.35, 35
• John Smith, 6.75, 33
• ________________________________
• Data stored in a file can be read in order (
  that is, sequentially) and assigned to variables
  with the following steps
• Choose a number from 1 to 255 to be the reference
  number for the file
• Execute the statement
• Open filenameFor Input As n
• Where n is the reference number
• The above procedure is referred to as opening a
  file for input. It establishes a communication
  link between the computer and the disk drive for
  reading data from the disk.

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• Read items of data in order, one at item, from
  the file with input statements. The statement
• Input n, var
• Causes the program to look in the file for the
  next available item of data and assign it to the
  variable var.
• In the file individual items are separated by
  commas or line breaks. The variable in the Input
  statement must be the same type as the data to
  be assigned to it from the file.
• 4. After the desired items have been read from
  the file, close the file with the statement
• Close n

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• Note A statement of the form
• Input n, var1, var2, , varj
• Has the same effect as the sequence of staments
• Input n, var1
• Input n, var2
• .
• Input n, varj
• Example The following program takes the average
  annual amounts of money spent by single-person
  households for several categories and converts
  these amounts to percentages.
• The form design for this example consists of a
  command button and a picture box.

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• _______________________________
• Transportation, 3887
• Housing, 7643
• Food, 3017
• Other, 7804
• _______________________________

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• Private Sub cmdCompute_Click()
• Dim total As Single, category As string, amount
  As Single
• Open COSTS.TXT For Input As 1
• PicPercent.Cls
• total0
• Input 1, category, amount
• total totalamount
• Input 1, category, amount
• total totalamount
• Input 1, category, amount
• total totalamount
• Input 1, category, amount
• total totalamount
• Close 1
• Open COSTS.TXT For Input As 1
• Input 1, category, amount
• PicPercent.Print category amount/total
• Input 1, category amount
• PicPercent.Print category amount/total

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• Run and then click the command button. The
  following is displayed in the picture box
• Transportation 0.1739072
• Housing 0.3419534
• Food 0.1349828
• Other 0.3491566
• Input from a Input Box
• Normally, a text box is used to obtain input
  described by a label. However, in some cases it
  is not practical to have a text box and label on
  the screen permanently.
• When a statement of the form
• stringVarInputBox(prompt, title)
• Is executed, an input box like this

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Pops up on the screen. After user types a
response into the text box at the bottom of
screen and press Enter (or clicks OK), the
response is assigned to the string variable
stringVar.
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• The title argument is optional and gives the
  caption to appear in title bar. The prompt
  argument is a string that ells the user what
  information to type into the text box.
• ExampleIn this example the file name is provided
  by the user in an input box.
• Run, and then click the command button. An input
  box appears on the screen. Type Data.Txt into the
  input box and click OK.
• ________________________
• 1600
• Pennsylvania Ave.
• ________________________
• Data.Txt

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• Private Sub cmdDisplay_Click()
• Dim fileName as String, prompt As String, title
  As String
• Dim houseNumber As Single, street As String
• picAddress.Cls
• promptEnter the name of the file containing
  the information.
• Title Name of the File
• fileNameInputBox(prompt, title)
• Open file Name For Input As 1
• Input 1, houseNumber
• Input 1, street
• picAddress.Print The white House is located
  at houseNumber street
• Close 1
• End Sub
• The White House is located at 1600 Pennsylvania
  Ave.

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• Using a Message Box for Output
• Some times you want to grab the users attention
  with a brief message such ascorrect. You want
  this message only to appear on the screen until
  the user has read it.
• When a statement of the form
• MsgBox prompt, , title
• Is executed, where prompt and title are strings,
  a message box with prompt displayed and the title
  bar caption title appears, and stay on the screen
  until the users presses Enter or clicks OK.
  Example
• MsgBox "Enter the name of a file", , "hi!
• produces

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Example

• The following program is going to use input
  boxes to allow the user to enter their name and
  age. It will do a simple calculation and print
  the results to a label. 
• The form looks like this

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•   Build the form according to the following
  specification
• Form Name frmAge
• Caption Age
• Command Button Name cmdExit
• Caption Exit
• Command Button Name cmdDetails
• Caption EnterDetails
• Command Button Name cmdResults
• Caption Print Results
• Label Name lblResults
• Border Style Fixed Single
• Caption none

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• Notice that the Caption property for each of the
  command buttons has an ampersand - a ''
  character - in it and this has the effect of
  underlining the letter that follows it. When you
  run the program, users now have a choice of using
  the mouse to click on a button or using a key
  combination. Let's see how it works...
• 1. Enter the code for the Exit button in the
  usual way
• 2. Run the program
• 3. Hold the ALT key and press the 'x' key
• So holding the ALT key and pressing the
  underlined letter has the same effect as clicking
  the button with a mouse. Clearly you must make
  sure that each button has a different letter
  that's underlined - you can't have two buttons
  with the same key combination.

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• we have two variables. The user's name is a
  string, or text, variable and we will call it
  UserName. The person's age is an integer and we
  will call it Age.
• If you've ever used a typewriter - well, we did
  say history - you'll know that when you want to
  start a new line, you have to do a line feed and
  a carriage return. The first of these moves the
  paper up a line and the second moves you to the
  start of the line.
• The upshot is that we really need to declare
  another variable called LFCR (Line Feed, Carriage
  Return) which we can use to do the job for us.
  You'll see how it works a little later but for
  now we need to declare all three variables in the
  General Declarations section of the project.
• Declare the variables like this

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• Here's the code for the cmdDetails Click event
• Private Sub cmdDetails_Click()
• UserName InputBox("Please enter your name")
• Age InputBox("please enter your age")
• End Sub
• Type in the code
• Run the program

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• Let's move now to the code for the Click event of
  the cmdResults button.
• Private Sub cmdResults_Click()
• Dim Days As Integer
• Dim TextOut As String
• LFCR Chr(10) Chr(13) 
• Days 365 Age
• 'build output string
• TextOut "Hello " UserName
• TextOut TextOut LFCR
• TextOut TextOut "You are at least "
• TextOut TextOut Str(Days)
• TextOut TextOut " days old!"
• lblResults.Caption TextOut
• End Sub

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• Enter the code and save your work
• Run the program and note what happens
• OK, let's go through this code, starting with
  these two lines
• Dim Days As Integer
• Dim TextOut As String
•  
• Nothing too mysterious here. We've declared Days
  as an integer and this is what we use for the
  person's age in days. We've also declared TextOut
  as a string and this is what we're going to use
  as the message to be printed out.

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• The line 
•  
• LFCR Chr(10) Chr(13)
• needs some explanation. Chr(10) is the linefeed
  character and Chr(13) is the carriage return
  character and so LFCR is a combination of the
  two, which we need when we print out the text in
  the label. All it does is move any following text
  onto a new line, just as if you'd pressed the
  ENTER key.
• Days 365 Age
• This calculates the number of days assuming that
  there are 365 days in a year

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•  The next line
• 'build output string
• doesn't in fact do anything and is ignored by the
  computer. It does however act as a comment to us
  and it is considered good practice to use
  comments in order to help other people understand
  your programs and make them more readable.
• And now to the following code
• TextOut "Hello " UserName
• TextOut TextOut LFCR
• TextOut TextOut "You are at least "
• TextOut TextOut Str(Days)
• TextOut TextOut " days old!"

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• The comment said it all really. We are building
  up a string, or piece of text, step by step. We
  start with the word "Hello " and we add the
  variable UserName, which we know is another piece
  of text
• . The line
• TextOut TextOut LFCR
•  
•  takes the string TextOut and adds to it our
  linefeed/carriage return combination. We proceed
  to add to the TextOut string as we go. There is a
  slight problem because, while UserName is a
  string, Days is an integer, and it doesn't make
  sense to add a number to a string - they are
  completely different data types. The way round
  it, though, is to use a special function called
  Str which Visual Basic has thoughtfully provided.
  It's job is to take a numerical value and convert
  it into a string, which we can then add to
  TextOut.

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• Finally, the line
• lblResults.Caption TextOut
• assigns our completed string to the Caption
  property of the label, and that's what you see
  printed out.