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Mastering File Operations in Visual Basic

Learn how to read data from files, execute open and close statements, and utilize dialog boxes for user input in Visual Basic. Explore functions like Input, Output, and Tab for effective programming.

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Mastering File Operations in Visual Basic

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  1. 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 Chapter 3 - Visual Basic Schneider

  3. Example of Reading from a File: Open “DATA.TXT” For Input As #1 Input #1,num1 Input #1, num2 picOutput.Print num1+num2  7 Close #1 Open the file Reference number Read the data and assign it to num1 Data.txt 3 4 Close the file Chapter 3 - Visual Basic Schneider

  4. Example of Reading from a File: Open “DATA.TXT” For Input As #1 Input #1,num1, num2 picOutput.Print num1+num2  7 Close #1 Data.txt 3 4 math.txt 2 4 5 8 5 6 Chapter 3 - Visual Basic Schneider

  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. Chapter 3 - Visual Basic Schneider

  6. 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 Chapter 3 - Visual Basic Schneider

  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 Chapter 3 - Visual Basic Schneider

  8. Example of a Message Dialog Box MsgBox "CS116", , "Visual Basic" Stays on the screen until the user presses OK

  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 Chapter 3 - Visual Basic Schneider

  12. Semicolons The next value output is placed in the next column position. Example: picOutput.Print “Patrick”; ”Jon” Output: PatrickJon Chapter 3 - Visual Basic Schneider

  13. Example of Semicolon picOutput.Print “Patrick”; “ Jon” Output Screen: Patrick Jon Space here Space here Chapter 3 - Visual Basic Schneider

  14. Example of Semicolon picOutput.Print 100; -200; 300 Output Screen: 100 -200 300 Two spaces One space Chapter 3 - Visual Basic Schneider

  15. 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. Chapter 3 - Visual Basic Schneider

  16. Using Commas Example: picOutput.Print “SEE”, ”YOU”, ”SOON” Output Screen: SEE YOU SOON Column 29 Column 15 Column 1 Chapter 3 - Visual Basic Schneider

  17. Using Commas Example: picOutput.Print “abc123def456ghi”, ”whatever” Output Screen: abc123def456ghi whatever Column 29 Column 15 Column 1 Chapter 3 - Visual Basic Schneider

  18. Using Commas A print zone can be skipped by typing consecutive commas Example: picOutput.Print “HOURLY”, , “PAY” Output Screen: HOURLY PAY Column 29 Chapter 3 - Visual Basic Schneider

  19. Cls: clears the form of all text PicBox.Cls: clears the PicBox of all text

  20. Private Sub cmdAdd_Click() picoutput.Print "1234567890123456789" picoutput.Print 10; 20; picoutput.Print -10, 30, picoutput.Print picoutput.Print 15; ; 6 picoutput.Print "Hello"; "hi"; picoutput.Print 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. 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) Chapter 3 - Visual Basic Schneider

  22. Example of Tab Function Example: picOutput.Print Tab(3); “Hi there!” ; Tab(25) ;“Bye!” Output Screen: Hi there! Bye! Column25 Column 3 Chapter 3 - Visual Basic Schneider

  23. Example of Tab Function Example: 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! Column 3 Column5 Chapter 3 - Visual Basic Schneider

  24. Tab

  25. 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) Chapter 3 - Visual Basic Schneider

  26. Numeric Functions Chapter 3 - Visual Basic Schneider

  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: 2.6 6 6.8 Chapter 3 - Visual Basic Schneider

  28. Something about Round with number 5 • Round( 123.75 , 1) • Round(12.45 , 1) • Round(3.5 , 0) • Round(4.5 , 0) • Round(4.52 , 0) • Round(23.57, 1 ) 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

  29. Commonly-Used String Functions Function: Left(“Penguin”, 4) Purpose: Returns the number of characters specified, starting at the beginning of the string Peng Chapter 3 - Visual Basic Schneider

  30. Commonly-Used String Functions Function: Right(“Gotham City”, 4) Purpose: Returns the number of characters specified from the end of the string City Chapter 3 - Visual Basic Schneider

  31. 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 Chapter 3 - Visual Basic Schneider

  32. Commonly-Used String Functions Function: UCase(“Yes”) Purpose: Converts any lowercase letters in a string to uppercase YES Chapter 3 - Visual Basic Schneider

  33. 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 Chapter 3 - Visual Basic Schneider

  34. String-Related Numeric Function Function: Len(“John Smith”) Purpose: Returns the number of characters in the string. 10 Chapter 3 - Visual Basic Schneider

  35. Strings and string Functions examples

  36. Example

  37. Example

  38. Format Functions The format functions provide detailed control of how numbers, dates, and strings are displayed. Examples FormatNumber (12345.678, 1) 12,345.7 FormatCurrency (12345.678, 2) $12,345.68 FormatPercent (.185, 2) 18.50% FormatNumber (1 + Sqr(2), 3) 2.414 Chapter 3 - Visual Basic Schneider

  39. 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). Example: picBox.Print Rnd +5 Output: Displays a random number from 5 to 6 (5 included and 6 excluded). Chapter 3 - Visual Basic Schneider

  40. Rnd Function Example: picBox.Print Int(Rnd) Output: Displays 0. Example: picBox.Print Int(Rnd +5) Output: Displays 5. Example: picBox.Print Int(Rnd) +5 Output: Displays 5. Chapter 3 - Visual Basic Schneider

  41. 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) Example: picBox.Print Int(5*Rnd) +2 Output: Displays a random Integer from 2 to 6 (2 and 6 included). Chapter 3 - Visual Basic Schneider

  42. Exercise: Revision • What will be dsiplayed in the picOutput when the user double click (click 2 times) on the command button cmdExample

  43. 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”))

  44. 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 Input #1,n s=s+n Input #1,n s=s+n close #1 print “s=”;s output: s= 60 data.txt 10 20 30

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

  47. 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

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

  49. Example

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