Section 3.5. Input and Output


[Page 105]

3.5. Input and Output

Formatting Output with Format Functions

The Format functions are used to display numbers in familiar forms and to align numbers. Here are some examples of how numbers are converted to strings with Format functions:

Function

String Value

FormatNumber(12345.628, 1)

12,345.6

FormatCurrency(12345.628, 2)

$12,345.63

FormatPercent(0.185, 2)

18.50%


The value of FormatNumber(n, r) is the string containing the number n rounded to r decimal places and displayed with commas as thousands separators. The value of FormatCurrency(n, r) is the string consisting of a dollar sign followed by the value of FormatNumber(n, r). FormatCurrency uses the accountant's convention of denoting negative amounts with surrounding parentheses. The value of FormatPercent(n, r) is the string consisting of the number n displayed as a percent and rounded to r decimal places. With all three functions, r can be omitted. If so, the number is rounded to two decimal places. Strings corresponding to numbers less than one in magnitude have a zero to the left of the decimal point. Also, n can be a number, a numeric expression, or even a string corresponding to a number.

Function

String Value

FormatNumber(1 + Math.Sqrt(2), 3)

2.414

FormatCurrency(1000)

($1,000.00)

FormatPercent(".05")

5.00%


Formatting Output with Zones

Data can be displayed in tabular form in a list box. In order to have the items line up nicely in columns, you must

  1. use a fixed-width font such as Courier New so that each character will have the same width;

  2. divide the line into zones with a format string.

Figure 3.21 (on the next page) shows a line of a list box divided into zones of widths 15 characters, 10 characters, and 8 characters. The leftmost zone is referred to as zone 0, the next zone is zone 1, and so on. These zones are declared in a string with the statement

Dim fmtStr As String = "{0, 15}{1, 10}{2, 8}"


Figure 3.21. Zones.
(This item is displayed on page 106 in the print version)


Note: The pairs of numbers are surrounded by curly brackets, not parentheses.


[Page 106]

If data0, data1, and data2 are strings or numbers, the statement

lstOutput.Items.Add(String.Format(fmtStr, data0, data1, data2))


displays the pieces of data right justified into the zones. If any of the width numbers 15, 10, or 8 is preceded with a minus sign, the data placed into the corresponding zone will be left justified.

Example 1.

The following program displays information about two colleges in the United States. Note: The endowments are in billions of dollars. The final column tells what fraction of the student body attended public secondary schools.

Object

Property

Setting

frmColleges

Text

College Data

lstColleges

Font

Courier New

btnDisplay

Text

Display Table


Private Sub btnDisplay_Click(...) Handles btnDisplay.Click   Dim fmtStr As String = "{0,-10}{1,12}{2,14}{3,12}"   With lstColleges.Items     .Clear()     .Add(String.Format(fmtStr, "College", "Enrollment", _                        "Endowment", "Public SS"))     .Add(String.Format(fmtStr, "Harvard", 6660, 19.2, 0.659))     .Add(String.Format(fmtStr, "Yale", 5278, 10.1, 0.532))   End With End Sub


[Run, and click on the button.]


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There is no limit to the number of zones, and the zones can be of any widths. In addition, by placing a colon and formatting symbols after the width, you can instruct Visual Basic to specially format numeric data. (String data are not affected.) The most used formatting symbols consist of a letter (n for number, C for currency, or P for percent) followed by a digit specifying the number of decimal places. If there is no digit after the letter, two decimal places are displayed. Here are some examples of such formatting:

Zone Format Term

Number to Be Formatted

Number Displayed

{1, 12:N3}

1234.5679

1,234.568

{1, 12:N0}

34.6

34

{1, 12:C1}

1234.567

$1,234.6

{1, 12:P}

0.569

56.90%


If the second line of the program in Example 1 is replaced with

Dim fmtStr As String = "{0,-10}{1,12:N0}{2,14:C}{3,12:P0}"


the output will be as follows.

The format strings considered so far consist of a sequence of pairs of curly brackets. We also can insert spaces between successive pairs of brackets. If so, the corresponding zones in the output will be separated by those spaces. The lines of code

Dim fmtStr As String = "{0, 5} {1, -5}" 'Two spaces after the                                       'first right curly bracket With lstOutput.Items   .Add("12345678901234567890")   .Add(String.Format(fmtStr, 1, 2)) End With


produce the output

12345678901234567890     1  2



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Reading Data from Files

So far, we have relied on assignment statements and text box controls to assign data to variables. Data also can be stored in files and accessed with a StreamReader object or supplied by the user with an input dialog box.

In Chapter 1, we saw how to create text files with Windows Notepad. We will assume that the files created with Notepad have one item of information per line. Figure 3.22 shows a sample file giving payroll information. Each set of three lines gives the name of a person, their hourly wage, and the number of hours that person worked during the week.

Figure 3.22. Contents of PAYROLL.TXT.

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:

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 communications 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 program. 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



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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()


Example 2.

Consider the following program that displays the address of the White House. (The form design for all examples in this section consists of a button and a text or list box.)

Private Sub btnDisplay_Click(...) Handles btnDisplay.Click   Dim houseNumber As Double   Dim street, address As String   houseNumber = 1600   street = "Pennsylvania Ave."   address = houseNumber & " " & street   txtAddr.Text = "The White House is located at " & address End Sub


[Run, and then click the button. The following is displayed in the text box.]

The White House is located at 1600 Pennsylvania Ave.


Let's now rewrite this program so that it uses a file for input and produces the same output. First, use Windows Notepad to create the file DATA.TXT containing the following two lines:

1600 Pennsylvania Ave.


In the following code, the fifth line of the event procedure reads the first row of data as the string "l600", converts its type to Double, and assigns it to the variable houseNumber. (Visual Basic records that this row of data has been used.) The sixth line looks for the next available line of data, "Pennsylvania Ave.", and assigns it to the string variable street.

Note: You will have to alter the information inside the parentheses in the second line to tell Visual Basic where the file DATA.TXT is located. For instance, if the file is in the root folder of a diskette in drive A, then the parentheses should contain the string "A:\DATA.TXT". If the file is located in the subfolder My Programs of the C drive, then the parentheses should contain the string "C:\My Programs\DATA.TXT". In this book, we will always write just the name of the file and leave it up to you to add an appropriate path.


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Private Sub btnDisplay_Click(...) Handles btnDisplay.Click   Dim sr As IO.StreamReader = IO.File.OpenText("DATA.TXT")   Dim houseNumber As Double   Dim street, address As String   houseNumber = CDbl(sr.ReadLine)   street = sr.ReadLine   sr.Close()   address = houseNumber & " " & street   txtAddr.Text = "The White House is located at " & address End Sub


Each Visual Basic program is contained in a folder with the name you specified in the Save Project window. This folder holds the files for the program and contains three subfolders named bin, My Project, and obj. The folder bin contains two subfolders named Debug and Release. If no path is specified for a text file, Visual Basic will look for the file in the Debug subfolder for the program. Every program from the companion website for this book that reads a file assumes that the file is located in the Debug subfolder for the program. Therefore, even after you copy the contents of the Programs folder onto a hard drive, the programs will continue to execute properly without your having to alter any paths.

Example 3.
(This item is displayed on pages 110 - 111 in the print version)

The following program uses the file PAYROLL.TXT shown in Figure 3.22.

Private Sub btnCompute_Click(...) Handles btnCompute.Click   Dim sr As IO.StreamReader = IO.File.OpenText("PAYROLL.TXT")   'The file PAYROLL.TXT is in the Debug subfolder   'of the bin subfolder of the folder 3-5-3.   Dim name As String   Dim hourlyWage, hoursWorked, salary As Double   name = sr.ReadLine   hourlyWage = CDbl(sr.ReadLine)   hoursWorked = CDbl(sr.ReadLine)   salary = hourlyWage * hoursWorked   lstPayroll.Items.Add(name & "   " & FormatCurrency(salary))   name = sr.ReadLine   hourlyWage = CDbl(sr.ReadLine)   hoursWorked = CDbl(sr.ReadLine)   sr.Close()   salary = hourlyWage * hoursWorked   lstPayroll.Items.Add(name & "   " & FormatCurrency(salary)) End Sub



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[Run, and then click the button. The following is displayed in the list box.]

Mike Jones $257.25 John Smith $222.75


In certain situations, we must read the data in a file more than once. This is accomplished by reopening the file with a second assignment statement of the form sr = IO.File.OpenText(filespec). This statement sets a pointer to the first line of data in the specified file. Each time a ReadLine method is executed, the line pointed to is read, and the pointer in then moved to the next line. After the last line of data is read, the pointer is said to be at the end of the file.

Example 4.
(This item is displayed on pages 111 - 112 in the print version)

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 data are read once to compute the total amount of money spent and then read again to calculate the percentage for each category. Note: These figures were compiled for a recent year by the Bureau of Labor Statistics.

The file COSTS.TXT consists of the following eight lines:

Transportation

4251

Housing

8929

Food

3414

Other

8829

Private Sub btnCompute_Click(...) Handles btnCompute.Click   Dim sr As IO.StreamReader = IO.File.OpenText("COSTS.TXT")   Dim total As Double            'Total annual amount spent   Dim category As String   Dim amount As Double          'Amount spent on category   Dim fmtStr As String = "{0,-15}{1,8:P}"   category = sr.ReadLine         'Read the first category from the file   total += CDbl(sr.ReadLine)     'Increment total by the amount                                 'associated with the category   category = sr.ReadLine         'Read the next category from the file   total += CDbl(sr.ReadLine)   category = sr.ReadLine   total += CDbl(sr.ReadLine)   category = sr.ReadLine   total += CDbl(sr.ReadLine)   sr.Close() 
[Page 112]
sr = IO.File.OpenText("COSTS.TXT") 'Open the file anew category = sr.ReadLine amount = CDbl(sr.ReadLine) lstPercent.Items.Add(String.Format(fmtStr, category, amount / total)) category = sr.ReadLine amount = CDbl(sr.ReadLine) lstPercent.Items.Add(String.Format(fmtStr, category, amount / total)) category = sr.ReadLine amount = CDbl(sr.ReadLine) lstPercent.Items.Add(String.Format(fmtStr, category, amount / total)) category = sr.ReadLine amount = CDbl(sr.ReadLine) lstPercent.Items.Add(String.Format(fmtStr, category, amount / total)) sr.Close() End Sub


[Run, and then click the button. The following is displayed in the list box.]

Transportation       16.72 % Housing              34.12 % Food                 13.43 % Other                34.73 %


Getting Input from an Input Dialog Box

Normally, a text box is used to obtain input, where the type of information requested is specified in a label adjacent to the text box. Sometimes, we want just one piece of input and would rather not have a text box and label stay on the screen forever. The problem can be solved with an input dialog box. When a statement of the form

stringVar = InputBox(prompt, title)


is executed, an input dialog box similar to the one shown in Figure 3.23 pops up on the screen. After the user types a response into the text box at the bottom of the screen and presses Enter (or clicks OK), the response is assigned to the string variable. The title argument is optional and provides the text that appears in the Title bar. The prompt argument is a string that tells the user what information to type into the text box.

Figure 3.23. Sample input dialog box.



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When you type the opening parenthesis following the word InputBox, the editor displays a line containing the general form of the InputBox statement. See Figure 3.24. This feature of IntelliSense is called Parameter Info. Optional parameters are surrounded by square brackets. All the parameters in the general form of the InputBox statement are optional except for prompt.

Figure 3.24. Parameter Info feature of IntelliSense.


Example 5.

In the following enhancement to Example 2, the file name is provided by the user in an input dialog box. We assume that the program is contained in the subfolder Debug of the program folder.

Private Sub btnDisplay_Click(...) Handles btnDisplay.Click   Dim sr As IO.StreamReader   Dim fileName, prompt, title, street As String   Dim  houseNumber As Double   prompt = "Enter the name of the file containing the information."   title = "Name of File"   fileName = InputBox(prompt, title)   'We assume the file is located in the subfolder Debug   'of the bin subfolder of the folder 3-5-5.   sr = IO.File.OpenText(fileName)   houseNumber = CDbl(sr.ReadLine)   street = sr.ReadLine   sr.Close()   txtAddr.Text = "The White House is located at " & _                  houseNumber & " " & street & "." End Sub


[Run, and then click the button. The input dialog box of Figure 3.23 appears on the screen. Type "DATA.TXT" into the input dialog box, and click on OK. The input dialog box disappears, and the following appears in the text box.]

The White House is located at 1600 Pennsylvania Ave.



[Page 114]

The response typed into an input dialog 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 an input dialog box should be converted to a number with CDbl or CInt before being assigned to a numeric variable or used in a calculation. Just as with a text box or file, the typed data must be a literal. It cannot be a variable or an expression. For instance, num, 1/2, and 2+3 are not acceptable.

Using a Message Dialog Box for Output

Sometimes you want to grab the user's attention with a brief message such as "Correct" or "Nice try, but no cigar." You want this message only to appear on the screen until the user has read it. This task is easily accomplished with a message dialog box such as the one shown in Figure 3.25. When a statement of the form

Figure 3.25. Sample message dialog box.


MsgBox(prompt, 0, 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 statement

MsgBox("Nice try, but no cigar.", 0, "Consolation")


produces Figure 3.25. You can omit the zero and a value for title and just execute MsgBox(prompt). If you do, the Title bar will contain the name of the program and the rest of the message dialog box will appear as before.

Using a Masked Text Box for Input

Problems can arise when the wrong type of data is entered as input into a text box. For instance, if the user replies to the request for an age by entering "twenty-one" into a text box, the program can easily crash. Sometimes this type of predicament can be avoided by using a masked text box for input. (In later chapters, we will consider other ways of insuring the integrity of input.)

In the Toolbox, the icon for the MaskedTextBox control consists of a rectangle containing the two characters # and _. The most important property of a masked text box is the Mask property that can be used to restrict the characters entered into the box. Also, the Mask property can be used to show certain characters in the controlto give users a visual cue that they should be entering a phone number or a social security number, for example. Some possible settings for the Mask property are shown in Table 3.3. The first two settings can be selected from a list of specified options. The last three settings generalize to any number of digits, letters, or ampersands. If the Mask property is left blank, then the MaskedTextBox control is nearly identical to the TextBox control.


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Table 3.3. Some settings for the Mask property.

Setting

Effect

000-00-0000

The user can only enter a social security number.

000-0000

The user can only enter a phone number (without an area code).

(000)000-0000

The user can only enter a phone number (with an area code).

00/00/0000

The user can only enter a date.

0000000

The user can only enter a positive integer consisting of 7 digits.

LLLLL

The user can only enter a string consisting of 5 letters.

&&&&&&&&

The user can only enter a string consisting of 8 characters.


Suppose a form contains a masked text box whose Mask property has the setting 000-00-0000. When the program is run, the string "___-__-____" will appear in the masked text box. The user will be allowed to type a digit in place of each of the eight underscore characters. The hyphens cannot be altered, and no characters can be typed anywhere else in the masked text box.

During run time, the characters 0, L, and & in the setting for a Mask property are replaced by underscore characters that are place holders for digits, letters, and letters and/or spaces, respectively. When the characters "-", "(", ")", or "/" appear in a characters for a Mask property, they appear as themselves in the masked text box and cannot be altered. There are some other mask settings, but these seven will suffice for our purposes.

Figure 3.26 (a) shows a masked text box during design time. It looks like an ordinary text box. However, the Tasks button for the masked text box is used to set the Mask property rather than the Multiline property. Figure 3.26 (b) shows the result of clicking on the Tasks button. Then, clicking on "Set mask" brings up the Input Mask dialog box shown in Figure 3.27. (This input dialog box is the same input dialog box that is invoked when you click on the ellipses in the Mask property's setting box.) You can use this input dialog box to select a commonly used value for the Mask property, such as the social security number or phone number mask, or set and test a custom-designed mask you create with characters such as 0, &, and L. We will use the prefix mtxt for the names of masked dialog boxes.

Figure 3.26. The Masked TextBox control.



[Page 116]

Figure 3.27. Input dialog box used to set the Mask property of a masked text box.


Comments

The statement Dim sr As IO.StreamReader = IO.File.OpenText("DATA.TXT") will be used frequently in this book, albeit with a different file name each time. You can store this line of code (or any frequently used fragment of code) for later reuse by highlighting it and dragging it from the Code window into the Toolbox. To reuse the code, just drag it back from the Toolbox to the Code window. A copy of the code will remain in the Toolbox for further use. Alternately, you can click on the location in the Code window where you want the code to be inserted, and then double-click on the code in the Toolbox.

Practice Problems 3.5

1.

Is the statement

txtOutput.Text = FormatNumber(12345.628, 1)


correct, or should it be written

txtOutput.Text = CStr(FormatNumber(12345.628, 1))



[Page 117]
2.

What is the difference in the outcomes of the following two sets of code?

strVar = InputBox("How old are you?", "Age") numVar = CDbl(strVar) txtOutput.Text = numVar numVar = CDbl(InputBox("How old are you?", "Age") txtOutput.Text = numVar


Exercises 3.5

In Exercises 1 through 30, determine the output produced by the lines of code.

1.

txtOutput.Text = FormatNumber(1234.56, 0)


2.

txtOutput.Text = FormatNumber(-12.3456, 3)


3.

txtOutput.Text = FormatNumber(1234, 1)


4.

txtOutput.Text = FormatNumber(12345)


5.

txtOutput.Text = FormatNumber(0.012, 1)


6.

txtOutput.Text = FormatNumber(5 * (10 ^ -2), 1)


7.

txtOutput.Text = FormatNumber(-2/3)


8.

Dim numVar As Double = Math.Round(1.2345, 1) txtOutput.Text = FormatNumber(numVar)


9.

Dim numVar As Double = Math.Round(12345.9) txtOutput.Text = FormatNumber(numVar, 3)


10.

Dim numVar As Double = Math.Round(12.5) txtOutput.Text = FormatNumber(numVar, 0)


11.

Dim numVar As Double = Math.Round(11.5) txtOutput.Text = FormatNumber(numVar, 0)


12.

txtOutput.Text = FormatCurrency(1234.5)


13.

txtOutput.Text = FormatCurrency(12345.67, 0)


14.

txtOutput.Text = FormatCurrency(-1234567)


15.

txtOutput.Text = FormatCurrency(-0.225)


16.

txtOutput.Text = FormatCurrency(32 * (10 ^ 2))


17.

txtOutput.Text = FormatCurrency(4 / 5)


18.

txtOutput.Text = FormatPercent(0.04, 0)


19.

txtOutput.Text = FormatPercent(0.075)


20.

txtOutput.Text = FormatPercent(-.05, 3)


21.

txtOutput.Text = FormatPercent(1)


22.

txtOutput.Text = FormatPercent(0.01)


23.

txtOutput.Text = FormatPercent(2 / 3)


24.

txtOutput.Text = FormatPercent(3 / 4, 1)


25.

txtOutput.Text = "Pay to France " & FormatCurrency(27267622)


26.

txtOutput.Text = "Manhattan was purchased for " & FormatCurrency(24)



[Page 118]
27.

Dim popUSover24 As Double = 177.6    'Million Dim collegeGrads As Double = 45.5    'Million                                      '45.5/177.6 = 0.2561937 txtOutput.Text = FormatPercent(collegeGrads / popUSover24, 1) & _   " of the U.S. population 25+ years old are college graduates."


28.

Dim degrees As String = FormatNumber(1711500, 0) txtOutput.Text = degrees & " degrees were conferred."


29.

txtOutput.Text = "The likelihood of Heads is " & _                  FormatPercent(1 / 2, 0)


30.

txtOutput.Text = "Pi = " & FormatNumber(3.1415926536, 4)


In Exercises 31 through 40, determine the output produced by the lines of code. Assume that Courier New is the font for the list box.

31.

 Dim fmtStr As String = "{0,-5}{1,5}" With lstOutput.Items   .Add("12345678901234567890")   .Add(String.Format(fmtStr, 1, 2)) End With


32.

Dim fmtStr As String = "{0,5}{1,5}" With lstOutput.Items   .Add("12345678901234567890")   .Add(String.Format(fmtStr, 1, 2)) End With


33.

Dim fmtStr As String = "{0,5}{1,-5}" With lstOutput.Items   .Add("12345678901234567890")   .Add(String.Format(fmtStr, 1, 2)) End With


34.

Dim fmtStr As String = "{0,-5}{1,-5}" With lstOutput.Items   .Add("12345678901234567890")   .Add(String.Format(fmtStr, 1, 2)) End With


35.

Dim fmtStr As String = "{0,3}{1,10}" With lstOutput.Items   .Add("12345678901234567890")   .Add(String.Format(fmtStr, "A", "Alice")) End With



[Page 119]
36.

Dim fmtStr As String = "{0,-13}{1,-10}{2,-7:N0}" With lstOutput.Items   .Add("123456789012345678901234567890")   .Add(String.Format(fmtStr, "Mountain", "Place", "Ht (ft)"))   .Add(String.Format(fmtStr, "K2", "Kashmir", 28250)) End With


37.

Dim fmtStr As String = "{0,11} {1,-11}" 'Three spaces With lstOutput.Items   .Add("12345678901234567890")   .Add(String.Format(fmtStr, "College", "Mascot"))   .Add(String.Format(fmtStr, "Univ. of MD", "Terrapins"))   .Add(String.Format(fmtStr, "Duke", "Blue Devils")) End With


38.

'Toss coin twice Dim fmtStr As String = "{0,8} {1,-7:P0}" 'Two spaces With lstOutput.Items   .Clear()   .Add("12345678901234567890")   .Add(String.Format(fmtStr, "Number", "Percent"))   .Add(String.Format(fmtStr, "of Heads", "of time"))   .Add(String.Format(fmtStr, 0, 1 / 4))   .Add(String.Format(fmtStr, 1, 1 / 2))   .Add(String.Format(fmtStr, 2, 1 / 4)) End With


39.

'Elements in a 150 Pound Person Dim fmtStr As String = "{0,-7} {1,-7:N1} {2,-7:P1}" '2 spaces With lstOutput.Items   .Clear()   .Add("12345678901234567890")   .Add(String.Format(fmtStr, "Element", "Weight", "Percent"))   .Add(String.Format(fmtStr, "Oxygen", 97.5, 97.5 / 150))   .Add(String.Format(fmtStr, "Carbon", 27, 27 / 150)) End With


40.

Dim fmtStr As String = "{0,10} {1,-10:C0}" 'Three spaces With lstOutput.Items   .Clear()   .Add("12345678901234567890")   .Add(String.Format(fmtStr, "", "Tuition"))   .Add(String.Format(fmtStr, "College", "& Fees"))   .Add(String.Format(fmtStr, "Stanford", 24441))   .Add(String.Format(fmtStr, "Harvard", 25128)) End With



[Page 120]

In Exercises 41 through 52, assume that the file DATA.TXT (shown to the right of the code) has been accessed with the statement Dim sr As IO.StreamReader = IO.File.OpenText("DATA.TXT") and closed afterwards with the statement sr.Close(). Determine the output displayed by the lines of code.

41.

Dim num As Double                                DATA.TXT num = CDbl(sr.ReadLine)                          4 txtOutput.Text = CStr(num * num)


42.

 Dim word As String                                DATA.TXT word = sr.ReadLine                                speakable txtOutput.Text = "un" & word


43.

Dim strl, str2 As String                           DATA.TXT str1 = sr.ReadLine                                 base str2 = sr.ReadLine                                 ball txtOutput.Text = strl & str2


44.

Dim numl, num2, num3 As Double                      DATA.TXT num1 = CDbl(sr.ReadLine)                            3 num2 = CDbl(sr.ReadLine)                            4 num3 = CDbl(sr.ReadLine)                            5 txtOutput.Text = CStr((numl + num2) * num3)


45.

Dim yrOfBirth, curYr As Double                     DATA.TXT yrOfBirth = CDbl(sr.ReadLine)                      1986 curYr = CDbl(sr.ReadLine) 'Current year            2006 txtOutput.Text = "Age: " & curYr - yrOfBirth


46.

Dim strl, str2 As String                       DATA.TXT strl = sr.ReadLine                             A, my name is str2 = sr.ReadLine                             Alice txtOutput.Text = strl & " " & str2


47.

Dim building As String                         DATA.TXT Dim numRooms As Double                         White House building = sr.ReadLine                         132 numRooms = CDbl(sr.ReadLine) txtOutput.Text = "The " & building " has " & numRooms & " rooms."


48.

Dim major As String                            DATA.TXT Dim percent As Double                          Computer Science major = sr.ReadLine                            1.4 percent = CDbl(sr.ReadLine) txtOutput.Text = "In 2004, " & percent & _       "% of entering college freshmen majored in " & major & "."


49.

Dim num, sum As Double                         DATA.TXT sum = 0                                        123 num = CDbl(sr.ReadLine)                        321 sum += num num = CDbl(sr.ReadLine) sum += num txtOutput.Text = "Sum: "& sum



[Page 121]
50.

Dim grade, total, average As Double                DATA.TXT Dim numGrades As Integer                           85 total = 0                                          95 numGrades = 0 grade = CDbl(sr.ReadLine) total += grade       'Increase value of total by value of grade numGrades += 1       'Increase value of numGrades by 1 grade = CDbl(sr.ReadLine) total += grade   'Increase value of total by value of grade numGrades += 1   'Increase value of numGrades by 1 average = total / numGrades txtOutput.Text = "Average grade: " & average


51.

Dim college As String                          DATA.TXT college = sr.ReadLine                          Harvard lstOutput.Items.Add(college)                   Yale sr.Close() sr = IO.File.OpenText("DATA.TXT") college = sr.ReadLine lstOutput.Items.Add(college)


52.

Dim num As Integer, str As String                 DATA.TXT num = CInt(sr.ReadLine)                            4 str = sr.ReadLine                                  calling birds lstOutput.Items.Add(num & " " & str)               3 sr.Close()                                         French hens sr = IO.File.OpenText("DATA.TXT") num = CInt(sr.ReadLine) str = sr.ReadLine lstOutput.Items.Add(num & " " & str)


In Exercises 53 through 58, determine the output displayed.

53.

Dim bet As Double              'Amount bet at roulette bet = CDbl(InputBox("How much do you want to bet?", "Wager")) txtOutput.Text = "You might win " & 36 * bet & " dollars."


(Assume that the response is 10.)

54.

Dim word As String word = InputBox("Word to negate:", "Negatives") txtOutput.Text = "un" & word


(Assume that the response is "tied".)

55.

Dim lastName, message, firstName As String lastName = "Jones" message = "What is your first name Mr. " & lastName & "?" firstName = InputBox(message, "Name") txtOutput.Text = "Hello " & firstName & " " & lastName


(Assume that the response is "John".)


[Page 122]
56.

Dim intRate, doublingTime As Double 'Current interest rate, time to double intRate = CDbl(InputBox("Current interest rate?", "Interest")) doublingTime = 72 / intRate lstOutput.Items.Add("At the current interest rate, money will") lstOutput.Items.Add("double in " & doublingTime & " years.")


(Assume that the response is 4.)

In Exercises 57 and 58, write a line of code to carry out the task.

57.

Pop up a message dialog box with "Good Advice" in the title bar and the message "Keep cool, but don't freeze."

58.

Pop up a message dialog box with "Taking Risks Proverb" in the title bar and the message "You can't steal second base and keep one foot on first."

In Exercises 59 through 66, identify any errors. If the code refers to a file, assume that DATA.TXT (on the right of the code) already has been opened for input.

59.

Dim num As Double                            DATA.TXT num = CDbl(sr.ReadLine)                      1 + 2 txtOutput.Text = CStr(3 * num)


60.

'Each line triplet of DATA.TXT contains         DATA.TXT 'building, height, # of stories                 Sears Tower Dim building As String                          1454 Dim ht As Double                                110 Dim numStories As Integer                       Empire State Building lstOutput.Items.Clear()                         1250 building = sr.ReadLine                          102 ht = CDbl(sr.ReadLine) lstOutput.Items.Add(building & " is " & ht & " feet tall.") building = sr.ReadLine ht = CDbl(sr.ReadLine) lstOutput.Items.Add(building & " is " & ht & " feet tall.")


61.

Dim num As Double num = InputBox("Pick a number from 1 to 10.") txtOutput.Text = "Your number is " & num


62.

info = InputBox()


63.

Dim num As Double = FormatNumber(123456)  lstOutput.Items.Add(num)


64.

txtOutput.Text = FormatCurrency($1234)


65.

Dim fmtStr As String = "{0,20}{1,10}" lstOutput.Items.Add(fmtStr, "Washington", "George")


66.

MsgBox("Proof", "Pulitzer Prize for Drama")



[Page 123]

In Exercises 67 through 70, write an event procedure starting with a Private Sub btnCompute_Click(. . .) Handles btnCompute.Click statement, ending with an End Sub statement, and having one, two, or three lines for each step. Lines that display data should use the given variable names.

67.

The following steps display information about Americans' eating habits. Assume that the three lines of the file SODA.TXT contain the following data: soft drinks, million gallons, 23.

  1. Declare all variables used in step (c).

  2. Open the file SODA.TXT for input.

  3. Use ReadLine statements to assign values to the variables food, units, and quantityPerDay.

  4. Display a sentence giving the quantity of a food item consumed by Americans in one day.

68.

The following steps display the changes in majors for first-year college students from 2003 to 2004. Assume that file MAJORS.TXT consists of six lines containing the following data: Elementary Education, 4.9, 4.6, Psychology, 4.7, 4.6.

  1. Declare all variables used in the steps that follow.

  2. Open the file MAJORS.TXT for input.

  3. Use ReadLine statements to assign values to the variables major, percent03, and percent04.

  4. Display a sentence giving the change in the percentage of students majoring in a certain subject.

  5. Repeat steps (c) and (d).

69.

The following steps calculate the percent increase in a typical grocery basket of goods:

  1. Declare all variables used in the steps that follow.

  2. Assign 200 to the variable begOfYearPrice.

  3. Request the price at the end of the year with an input dialog box, and assign it to the variable endOfYearPrice.

  4. Assign 100*(endOfYearPrice begOfYearPrice) / begOfYearPrice to the variable percentIncrease.

  5. Display a sentence giving the percent increase for the year.

(Test the program with a $215 end-of-year price.)

70.

The following steps calculate the amount of money earned in a walk-a-thon:

  1. Declare all variables used in the steps that follow.

  2. Request the amount pledged per mile from an input dialog box, and assign it to the variable pledge.

  3. Request the number of miles walked from an input dialog box, and assign it to the variable miles.

  4. Display a sentence giving the amount to be paid.

(Test the program with a pledge of $2.00 and a 15-mile walk.)


[Page 124]

In Exercises 71 through 76, give a setting for the Mask property of a masked text box used to input the stated information.

71.

A number from 100 to 999.

72.

A word of ten letters.

73.

A Maryland license plate consisting of three letters followed by three digits. (Example: BHC365)

74.

A California license plate consisting of a digit followed by three letters and then three digits. (Example: 7BHC365)

75.

An ISBN number. [Every book is identified by a ten-character International Standard Book Number (ISBN). The first nine characters are digits and the last character is either a digit or the letter X.] (Example: 0-32-108599-X).

76.

A two-letter state abbreviation. (Example: CA)

77.

Table 3.4 summarizes the month's activity of three checking accounts. Write a program that displays the account number and the end-of-month balance for each account and then displays the total amount of money in the three accounts. Assume that the data are stored in a text file.

Table 3.4. Checking account activity.

Account Number

Beginning of Month Balance

Deposits

Withdrawals

AB4057

1234.56

345.67

100.00

XY4321

789.00

120.00

350.00

GH2222

321.45

143.65

0.00


78.

Table 3.5 contains a list of colleges with their student enrollments and faculty sizes. Write a program to display the names of the colleges and their student/faculty ratios, and the ratio for the total collection of students and faculty. Assume that the data for the colleges are stored in a text file.

Table 3.5. Colleges.
 

Enrollment

Faculty

Ohio State

50721

3657

Univ. of MD, College Park

35262

2087

Princeton

6849

1015

Source: The World Almanac, 2005.


79.

Write a program to compute semester averages. Each set of five lines in a text file should contain a student's Social Security number and the grades for three hourly exams and the final exam. (The final exam counts as two hourly exams.) The program should display each student's Social Security number and semester average, and then the class average. Use the data in Table 3.6.


[Page 125]

Table 3.6. Student grades.

Soc. Sec. No.

Exam 1

Exam 2

Exam 3

Final Exam

123-45-6789

67

85

90

88

111-11-1111

93

76

82

80

123-32-1234

85

82

89

84


80.

Table 3.7 gives the year 2003 populations of three New England states. Write a program that calculates the average population and then displays the name of each state and the difference between its population and the average population. The states and their populations should be stored in a text file.

Table 3.7. 2003 population (in thousands) of three New England states.

State

Population

Maine

1305

Massachusetts

6433

Connecticut

3483


81.

Design a form with two text boxes labeled "Name" and "Phone number". Then write an event procedure that shows a message dialog box stating "Be sure to include the area code!" when the second text box receives the focus.

82.

Write a program to calculate the amount of a waiter's tip given the amount of the bill and the percentage tip obtained via input dialog boxes. The output should be a complete sentence that reiterates the inputs and gives the resulting tip, as shown in Figure 3.28.

Figure 3.28. Sample output for Exercise 82.


83.

When P dollars are deposited in a savings account at interest rate r compounded annually, the balance after n years is P(1 + r)n. Write a program to request the principal P and the interest rate r as input, and compute the balance after 10 years, as shown in Figure 3.29 (on the next page).


[Page 126]

Figure 3.29. Sample output for Exercise 83.


In Exercises 84 and 85, write lines of code corresponding to the given flowchart. Assume that the data needed are contained in a file.

84.

85.


[Page 127]
Solutions to Practice Problems 3.5

1.

The first statement is correct, since FormatNumber evaluates to a string. Although the second statement is not incorrect, the use of CStr is redundant.

2.

The outcomes are identical. In this text, we primarily use the second style.




An Introduction to Programming Using Visual Basic 2005
Introduction to Programming Using Visual Basic 2005, An (6th Edition)
ISBN: 0130306541
EAN: 2147483647
Year: 2006
Pages: 164

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