1. Chapter 8 - Visual Basic Schneider
Chapter 3-B
Files and Functions
Chapter 8 - Visual Basic Schneider

2. 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
1. The name of the file: follows the same rules for naming program files.
Use invest.bas and invest.dat
2. The mode in which the file is to be used , can be output, input, append .
Output: indicates data is written to the file from the program
input: the contents of the file are being read into the program
append :allows new records to be added to an existing file.
A butter is a reserved part of the primary storage unit used a s temporary storage area for the data that is being written or read from a file
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3. Example of Reading from a File:
Open the file
Open “DATA.TXT” For Input As #1
Input #1, num1
Input #1, num2
picOutput.Print num1+num2  7
Close #1
Reference number
Read the data and assign it to num1
Data.txt
A file can have either one item per line or many items (separated by commas) can be listed on the same line
the items of data will be assigned to variables one at the time in the order they appear in the file.
1. Choose a number from 1 to 255 to be the reference number for the file
2. Open the file for input
3. Read items of data in order, one at the time, from the file with Input sattement
Show Examples: Path is C;\F98 CSE181\Examples\Ch3\Data.txt
The response typed into an input box is treated as a single string value, no matter what is typed. Quotation marks are not needed, and if included, are considered as part of the string.
Numeric data typed into n input box should be converted to a number with Val before it is assigned to a numeric variable or used in calculation.
Close the file 3 4
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4. Example of Reading from a File:
Data.txt
Open “DATA.TXT” For Input As #1
Input #1, num1, num2
picOutput.Print num1+num2  7
Close #1 3 4
math.txt
2 4 5 8 5 6
Example #1: create a file named Student.dat
Prepare the file to receive data
If a file already exists, it is destroyed and a new file is created.
Associated with the file Student.date with buffer #1. As long as the file is open. Buffer #1 is used temporarily before the data is written to the file on disk
Other statement in the program use this number to identify the file..
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5. Reading Data from Files
Files can be also used for output rather than input. More about files will be discussed in chapter 8 and 9.
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6. Chapter 3 - Visual Basic Schneider
Input Dialog Box
An input dialog box can be used to obtain a single item of input from the user
Presents a window (dialog box) requesting input
Syntax:
stringVar = InputBox(prompt, title)
Note:The type of inputBox is string type
After users types in a response into the rectangle at the bottom of the screen and press Enter, the response is assigned to the string variable.
Normally, text box is used to obtain input, sometimes we want just one piece of input and would rather not have a text box and label stay on the screen for ever.
Example
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7. Using Message Dialog Box for Output
The message dialog box is used to present a pop-up window containing information for the user
Syntax: MsgBox prompt, , title
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8. Example of a Message Dialog Box
MsgBox "CS116", , "Visual Basic"
Stays on the
screen until the
user presses OK
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9. Example of a Message Dialog Box
MsgBox "CS116"

10. Example

11. 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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12. Chapter 3 - Visual Basic Schneider
Semicolons
The next value output is placed in the next column position.
Example:
picOutput.Print “Patrick”; ”Jon”
Output:
PatrickJon
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13. Chapter 3 - Visual Basic Schneider
Example of Semicolon
picOutput.Print “Patrick”; “ Jon”
Output Screen:
Patrick Jon
Space here
Space here
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14. Chapter 3 - Visual Basic Schneider
Example of Semicolon
picOutput.Print 100; -200; 300
Output Screen:
Two spaces
One space
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15. Chapter 3 - Visual Basic Schneider
Commas
A comma in a Print method 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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16. Chapter 3 - Visual Basic Schneider
Using Commas
Example:
picOutput.Print “SEE”, ”YOU”, ”SOON”
Output Screen:
SEE YOU SOON
See in column 1 Y in column 15 and S in column 29
Column 29
Column 15
Column 1
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17. Chapter 3 - Visual Basic Schneider
Using Commas
Example:
picOutput.Print “abc123def456ghi”, ”whatever”
Output Screen:
abc123def456ghi whatever
See in column 1 Y in column 15 and S in column 29
Column 29
Column 15
Column 1
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18. Chapter 3 - Visual Basic Schneider
Using Commas
A print zone can be skipped by typing consecutive commas
Example:
picOutput.Print “HOURLY”, , “PAY”
Output Screen:
HOURLY PAY
Example 3.5.5
Column 29
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19. Cls: clears the form of all text
PicBox.Cls: clears the PicBox of all text

20. Private Sub cmdAdd_Click()
picoutput.Print " "
picoutput.Print 10; 20;
picoutput.Print -10, 30,
picoutput.Print
picoutput.Print 15; ; 6
picoutput.Print "Hello"; "hi";
picoutput.Print "12345", "12"
End Sub
;  in the next position column position
,  in the next available print zone
picOutput.Print  moves the cursor to the beginning of the next line

21. Chapter 3 - Visual Basic Schneider
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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22. Example of Tab Function
picOutput.Print Tab(3); “Hi there!” ; Tab(25) ;“Bye!”
Output Screen:
Hi there! Bye!
Example 3.5.6
Organizes data into columns of a table
Column 25
Column 3
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23. Example of Tab Function
picOutput.Print Tab(3); “Hi there!” ; Tab(5) ;“Bye!”
Because column 5 is already occupied by the previous string, the output will be at the next line
Output Screen:
Hi there!
Bye!
Example 3.5.6
Organizes data into columns of a table
Column 3
Column 5
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24. Tab

25. Chapter 3 - Visual Basic Schneider
Built-In Functions
Take one or more input values and return an output value
A means provided by Visual Basic for carrying out small, common tasks
Types of Built-In functions
Numeric functions (manipulate numbers)
String functions (manipulate strings)
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26. Chapter 3 - Visual Basic Schneider
Numeric Functions
Example for Int function and Sqr function
Example : rounds a positive number to the nearest integer..
To round a number t two decimal places
r = Int (100*n + 0.5) / 100
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27. Example of Numeric Functions
Private Sub cmdEvaluate_Click()
Dim n As Single, root As Single
n = 6.76
root = Sqr(n)
picResults.Print root; Int(n); Round(n,1)
End Sub
Output:
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29. Something about Round with number 5
123.8
12.4 4 4 5
23.6
Note that to round a number that is followed by number 5 and nothing after number 5, if it is odd make the round, if it is even number don’t round

30. Commonly-Used String Functions
Function: Left(“Penguin”, 4)
Purpose: Returns the number of characters specified, starting at the beginning of the string
Peng
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31. Commonly-Used String Functions
Function: Right(“Gotham City”, 4)
Purpose: Returns the number of characters specified from the end of the string
City
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32. Commonly-Used String Functions
Function: Mid(“Commissioner”, 4, 3)
Purpose: Returns the substring starting at the position indicated by the first number and continuing for the length specified by the second number
mis
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33. Commonly-Used String Functions
Function: UCase(“Yes”)
Purpose: Converts any lowercase letters in a string to uppercase
YES
Go over Example 6 page 121
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34. String-Related Numeric Functions
Function: InStr(“John Smith”, “m”)
Purpose: Searches for the first occurrence of one string in another and gives the position at which the string is found 7
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35. String-Related Numeric Function
Function: Len(“John Smith”)
Purpose: Returns the number of characters in the string. 10
Is 10
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36. Strings and string Functions examples

37. Example

38. Example

39. Chapter 3 - Visual Basic Schneider
Format Functions
The format functions provide detailed control of how numbers, dates, and strings are displayed.
Examples
FormatNumber ( , 1) ,345.7
FormatCurrency ( , 2) $12,345.68
FormatPercent (.185, 2) %
FormatNumber (1 + Sqr(2), 3)
Numbers can be made to line up uniformly and be displayed with dollar signs, commas and a specified number of decimal places. Dates can be converted
to a long or medium form. Strings can be right justified.
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40. Chapter 3 - Visual Basic Schneider
Rnd Function
Returns a random number from 0 to 1.
(excluding 1).
Example:
picBox.Print Rnd
Output: Displays a random number from 0 to 1 (0 included and 1 excluded).
picBox.Print Rnd +5
Output: Displays a random number from 5 to 6 (5 included and 6 excluded).
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41. Chapter 3 - Visual Basic Schneider
Rnd Function
Example:
picBox.Print Int(Rnd)
Output: Displays 0.
picBox.Print Int(Rnd +5)
Output: Displays 5.
picBox.Print Int(Rnd) +5
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42. Chapter 3 - Visual Basic Schneider
Rnd Function
Example:
picBox.Print Int(5*Rnd)
Output: Displays a random Integer from 0 to 4 (0 and 4 included). OR
Output: Displays a random Integer from 0 to 5 (0 included and 5 excluded)
picBox.Print Int(5*Rnd) +2
Output: Displays a random Integer from 2 to 6 (2 and 6 included).
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43. Exercise: Revision
What will be dsiplayed in the picOutput when the user double click (click 2 times) on the command button cmdExample

44. Exercises:
Position the location of the form at run time  Form layout windows
To open a file called “data.txt” located in C:\VB folder you must write
 Open “C:\VB\data.txt” for input as #1
Which of the following statement assign the content of the input box to a numeric variable X
X = Val(InputBox(“Enter the number”))

45. What is the output of the following code?
Dim s as integer, n as integer
Open “data.txt” for Input as #1
Input #1,n
s=s+n
close #1
print “s=”;s
output: s= 60
data.txt 10 20 30

46. what is output of the following code?
Dim n as integer
Open “data.txt” for Input as #1
Input #1,n
Close #1
Print “n = ”; n
Output:
n = 20
data.txt 10 20 30

47. what is output of the following code?
Dim n as integer
Open “data.txt” for Input as #1
Input #1,n
Close #1
Print “n = ”; n
Output:
n = 10
data.txt 10 20 30

48. Syntax Errors (Compile Errors)
Grammatical errors, such as misspelling, are called syntax error. Syntax error is encountered during compilation (by Complier)
picBox.Primt 3
9W = 5
picBox.Print 2-
If x > 10
x = x+1
End If

49. Run-time errors
Errors that occur while a program is running are called run-time errors
Division by zero
File not found

50. Example

51. Logical errors
Occurs when a program dose not perform the way it was intended
A program with a logic error is a valid program in the language, though it does not behave as intended.
Average = num1 + num2 / 2

52. Debugging
The process of finding and correcting errors

53. Chapter 3 - Visual Basic - Schneider
Reference
Chapter 3 - Visual Basic - Schneider