cs 4 intro to programming using visual basic

1: CS 4 Intro to Programming using Visual Basic Input Output Patchrawat UthaisombutUniversity of Pittsburgh 1

2: Chapter 3 - VB 2005 by Schneider 2

3: Chapter 3 - VB 2005 by Schneider 3 Formatting Output with Format Functions

4: Chapter 3 - VB 2005 by Schneider 4 Formatting Output with Zones Use a fixed-width font such as Courier New Divide the characters into zones with a format string. Dim fmtStr As String = "{0, 15}{1, 10}{2, 8}" lstOutput.Items.Add(String.Format(fmtStr, _ data0, data1, data2))

5: Chapter 3 - VB 2005 by Schneider 5 Formatting Output with Zones Dim fmtStr As String = "{0, -15}{1, 10}{2, 8}" lstOutput.Items.Add(String.Format(fmtStr, _ data0, data1, data2)) Here, 15 was preceded by a minus sign. This produces left justification in 0th zone. There will be right justification in the other two zones.

6: Chapter 3 - VB 2005 by Schneider 6 Zone Formatting Symbols

7: Chapter 3 - VB 2005 by Schneider 7 Reading Data from Files Data can be stored in files and accessed with a StreamReader object. We assume that the files are text files (that is, have extension .TXT) and have one piece of data per line.

8: Chapter 3 - VB 2005 by Schneider 8 Sample File: PAYROLL.TXT Mike Jones 7.35 35 John Smith 6.75 33

9: Chapter 3 - VB 2005 by Schneider 9 Steps to Use StreamReader Execute a statement of the form Dim readerVar As IO.StreamReader = _ IO.File.OpenText(filespec) or the pair of statements Dim readerVar As IO.StreamReader readerVar = IO.File.OpenText(filespec) 1. Execute a statement of the form Dim readerVar As IO.StreamReader A StreamReader is an object from the Input/Output class that can read a stream of characters coming from a disk or coming over the Internet. The Dim statement declares the variable readerVar to be of type StreamReader. 2. Execute a statement of the form readerVar = IO.File.OpenText(filespec) where filespec identifies the file to be read. This statement establishes a communi-cations link between the computer and the disk drive for reading data from the disk. Data then can be input from the specified file and assigned to variables in the pro-gram. This assignment statement is said to “open the file for input.” Just as with other variables, the declaration and assignment statements in Steps 2 and 3 can be combined into the single statement Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec) 3. Read items of data in order, one at a time, from the file with the ReadLine method. Each datum is retrieved as a string. A statement of the form strVar = readerVar.ReadLine causes the program to look in the file for the next unread line of data and assign it to the variable strVar. The data can be assigned to a numeric variable if it is first converted to a numeric type with a statement such as numVar = CDbl(readerVar.ReadLine) Note: If all the data in a file have been read by ReadLine statements and another item is requested by a ReadLine statement, the item retrieved will have the value Nothing. 4. After the desired items have been read from the file, terminate the communications link set in Step 3 with the statement readerVar.Close()1. Execute a statement of the form Dim readerVar As IO.StreamReader A StreamReader is an object from the Input/Output class that can read a stream of characters coming from a disk or coming over the Internet. The Dim statement declares the variable readerVar to be of type StreamReader. 2. Execute a statement of the form readerVar = IO.File.OpenText(filespec) where filespec identifies the file to be read. This statement establishes a communi-cations link between the computer and the disk drive for reading data from the disk. Data then can be input from the specified file and assigned to variables in the pro-gram. This assignment statement is said to “open the file for input.” Just as with other variables, the declaration and assignment statements in Steps 2 and 3 can be combined into the single statement Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec) 3. Read items of data in order, one at a time, from the file with the ReadLine method. Each datum is retrieved as a string. A statement of the form strVar = readerVar.ReadLine causes the program to look in the file for the next unread line of data and assign it to the variable strVar. The data can be assigned to a numeric variable if it is first converted to a numeric type with a statement such as numVar = CDbl(readerVar.ReadLine) Note: If all the data in a file have been read by ReadLine statements and another item is requested by a ReadLine statement, the item retrieved will have the value Nothing. 4. After the desired items have been read from the file, terminate the communications link set in Step 3 with the statement readerVar.Close()

10: Chapter 3 - VB 2005 by Schneider 10 Steps to Use StreamReader Read items of data in order, one at a time, from the file with the ReadLine method. strVar = readerVar.ReadLine After the desired items have been read from the file, terminate the communications link readerVar.Close() 1. Execute a statement of the form Dim readerVar As IO.StreamReader A StreamReader is an object from the Input/Output class that can read a stream of characters coming from a disk or coming over the Internet. The Dim statement declares the variable readerVar to be of type StreamReader. 2. Execute a statement of the form readerVar = IO.File.OpenText(filespec) where filespec identifies the file to be read. This statement establishes a communi-cations link between the computer and the disk drive for reading data from the disk. Data then can be input from the specified file and assigned to variables in the pro-gram. This assignment statement is said to “open the file for input.” Just as with other variables, the declaration and assignment statements in Steps 2 and 3 can be combined into the single statement Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec) 3. Read items of data in order, one at a time, from the file with the ReadLine method. Each datum is retrieved as a string. A statement of the form strVar = readerVar.ReadLine causes the program to look in the file for the next unread line of data and assign it to the variable strVar. The data can be assigned to a numeric variable if it is first converted to a numeric type with a statement such as numVar = CDbl(readerVar.ReadLine) Note: If all the data in a file have been read by ReadLine statements and another item is requested by a ReadLine statement, the item retrieved will have the value Nothing. 4. After the desired items have been read from the file, terminate the communications link set in Step 3 with the statement readerVar.Close()1. Execute a statement of the form Dim readerVar As IO.StreamReader A StreamReader is an object from the Input/Output class that can read a stream of characters coming from a disk or coming over the Internet. The Dim statement declares the variable readerVar to be of type StreamReader. 2. Execute a statement of the form readerVar = IO.File.OpenText(filespec) where filespec identifies the file to be read. This statement establishes a communi-cations link between the computer and the disk drive for reading data from the disk. Data then can be input from the specified file and assigned to variables in the pro-gram. This assignment statement is said to “open the file for input.” Just as with other variables, the declaration and assignment statements in Steps 2 and 3 can be combined into the single statement Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec) 3. Read items of data in order, one at a time, from the file with the ReadLine method. Each datum is retrieved as a string. A statement of the form strVar = readerVar.ReadLine causes the program to look in the file for the next unread line of data and assign it to the variable strVar. The data can be assigned to a numeric variable if it is first converted to a numeric type with a statement such as numVar = CDbl(readerVar.ReadLine) Note: If all the data in a file have been read by ReadLine statements and another item is requested by a ReadLine statement, the item retrieved will have the value Nothing. 4. After the desired items have been read from the file, terminate the communications link set in Step 3 with the statement readerVar.Close()

11: Chapter 3 - VB 2005 by Schneider 11 Example using StreamReader Dim name As String Dim wage, hours As Double Dim sr As IO.StreamReader = _ IO.File.OpenText("PAYROLL.TXT") name = sr.ReadLine wage = CDbl(sr.ReadLine) hours = CDbl(sr.ReadLine) lstBox.Items.Add(name & ": " & wage * hours) OUTPUT: Mike Jones: 257.25 1. Execute a statement of the form Dim readerVar As IO.StreamReader A StreamReader is an object from the Input/Output class that can read a stream of characters coming from a disk or coming over the Internet. The Dim statement declares the variable readerVar to be of type StreamReader. 2. Execute a statement of the form readerVar = IO.File.OpenText(filespec) where filespec identifies the file to be read. This statement establishes a communi-cations link between the computer and the disk drive for reading data from the disk. Data then can be input from the specified file and assigned to variables in the pro-gram. This assignment statement is said to “open the file for input.” Just as with other variables, the declaration and assignment statements in Steps 2 and 3 can be combined into the single statement Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec) 3. Read items of data in order, one at a time, from the file with the ReadLine method. Each datum is retrieved as a string. A statement of the form strVar = readerVar.ReadLine causes the program to look in the file for the next unread line of data and assign it to the variable strVar. The data can be assigned to a numeric variable if it is first converted to a numeric type with a statement such as numVar = CDbl(readerVar.ReadLine) Note: If all the data in a file have been read by ReadLine statements and another item is requested by a ReadLine statement, the item retrieved will have the value Nothing. 4. After the desired items have been read from the file, terminate the communications link set in Step 3 with the statement readerVar.Close()1. Execute a statement of the form Dim readerVar As IO.StreamReader A StreamReader is an object from the Input/Output class that can read a stream of characters coming from a disk or coming over the Internet. The Dim statement declares the variable readerVar to be of type StreamReader. 2. Execute a statement of the form readerVar = IO.File.OpenText(filespec) where filespec identifies the file to be read. This statement establishes a communi-cations link between the computer and the disk drive for reading data from the disk. Data then can be input from the specified file and assigned to variables in the pro-gram. This assignment statement is said to “open the file for input.” Just as with other variables, the declaration and assignment statements in Steps 2 and 3 can be combined into the single statement Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec) 3. Read items of data in order, one at a time, from the file with the ReadLine method. Each datum is retrieved as a string. A statement of the form strVar = readerVar.ReadLine causes the program to look in the file for the next unread line of data and assign it to the variable strVar. The data can be assigned to a numeric variable if it is first converted to a numeric type with a statement such as numVar = CDbl(readerVar.ReadLine) Note: If all the data in a file have been read by ReadLine statements and another item is requested by a ReadLine statement, the item retrieved will have the value Nothing. 4. After the desired items have been read from the file, terminate the communications link set in Step 3 with the statement readerVar.Close()

12: Chapter 3 - VB 2005 by Schneider 12 Comment on Example Consider lstBox.Items.Add(name & ": " & wage * hours) The ampersand automatically converted wage * hours into a string before concatenating. We didn’t have to convert wage * hours with CStr. 1. Execute a statement of the form Dim readerVar As IO.StreamReader A StreamReader is an object from the Input/Output class that can read a stream of characters coming from a disk or coming over the Internet. The Dim statement declares the variable readerVar to be of type StreamReader. 2. Execute a statement of the form readerVar = IO.File.OpenText(filespec) where filespec identifies the file to be read. This statement establishes a communi-cations link between the computer and the disk drive for reading data from the disk. Data then can be input from the specified file and assigned to variables in the pro-gram. This assignment statement is said to “open the file for input.” Just as with other variables, the declaration and assignment statements in Steps 2 and 3 can be combined into the single statement Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec) 3. Read items of data in order, one at a time, from the file with the ReadLine method. Each datum is retrieved as a string. A statement of the form strVar = readerVar.ReadLine causes the program to look in the file for the next unread line of data and assign it to the variable strVar. The data can be assigned to a numeric variable if it is first converted to a numeric type with a statement such as numVar = CDbl(readerVar.ReadLine) Note: If all the data in a file have been read by ReadLine statements and another item is requested by a ReadLine statement, the item retrieved will have the value Nothing. 4. After the desired items have been read from the file, terminate the communications link set in Step 3 with the statement readerVar.Close()1. Execute a statement of the form Dim readerVar As IO.StreamReader A StreamReader is an object from the Input/Output class that can read a stream of characters coming from a disk or coming over the Internet. The Dim statement declares the variable readerVar to be of type StreamReader. 2. Execute a statement of the form readerVar = IO.File.OpenText(filespec) where filespec identifies the file to be read. This statement establishes a communi-cations link between the computer and the disk drive for reading data from the disk. Data then can be input from the specified file and assigned to variables in the pro-gram. This assignment statement is said to “open the file for input.” Just as with other variables, the declaration and assignment statements in Steps 2 and 3 can be combined into the single statement Dim readerVar As IO.StreamReader = IO.File.OpenText(filespec) 3. Read items of data in order, one at a time, from the file with the ReadLine method. Each datum is retrieved as a string. A statement of the form strVar = readerVar.ReadLine causes the program to look in the file for the next unread line of data and assign it to the variable strVar. The data can be assigned to a numeric variable if it is first converted to a numeric type with a statement such as numVar = CDbl(readerVar.ReadLine) Note: If all the data in a file have been read by ReadLine statements and another item is requested by a ReadLine statement, the item retrieved will have the value Nothing. 4. After the desired items have been read from the file, terminate the communications link set in Step 3 with the statement readerVar.Close()

13: Chapter 3 - VB 2005 by Schneider 13 Getting Input from an Input Dialog Box stringVar = InputBox(prompt, title) fileName = InputBox("Enter the name " _ & "of the file containing the " & _ "information.", "Name of File")

14: Chapter 3 - VB 2005 by Schneider 14 Using a Message Dialog Box for Output MsgBox(prompt, 0, title) MsgBox("Nice try, but no cigar.", 0, _ "Consolation") MsgBox(prompt, , title) is executed, where prompt and title are strings, a message dialog box appears with prompt displayed and the title bar caption title and stays on the screen until the user presses Enter, clicks on the box in the upper-right corner, or clicks OK. For instance, the state-ment MsgBox("Nice try, but no cigar.", , "Consolation")MsgBox(prompt, , title) is executed, where prompt and title are strings, a message dialog box appears with prompt displayed and the title bar caption title and stays on the screen until the user presses Enter, clicks on the box in the upper-right corner, or clicks OK. For instance, the state-ment MsgBox("Nice try, but no cigar.", , "Consolation")

15: Chapter 3 - VB 2005 by Schneider 15 Masked Text Box

16: Chapter 3 - VB 2005 by Schneider 16 Input Mask Dialog Box

17: Chapter 3 - VB 2005 by Schneider 17 Mask

18: Chapter 3 - VB 2005 by Schneider 18 Sample Masks