Computer Programming Concepts and Visual Basic David I. Schneider

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36 Computer Programming Concepts and Visual Basic ■ SCIENTIFIC NOTATION Let us review powers of 10 and scientific notation. Our method of decimal notation is based on a systematic use of exponents. 10 1 = 10 10 –1 = 1/10 = .1 10 2 = 100 10 –2 = .01 10 3 = 1000 10 –3 = .001 . . . 10 n = 1000...0 10 –n = .001...01 n zeros n digits Scientific notation provides a convenient way of writing numbers by using powers of 10 to stand for zeros. Numbers are written in the form b � 10 r , where b is a number from 1 up to (but not including) 10, and r is an integer. For example, it is much more convenient to write the diameter of the sun (1,400,000,000 meters) in scientific notation: 1.4 � 10 9 meters. Similarly, rather than write .0000003 meters for the diameter of a bacterium, it is simpler to write 3 � 10–7 meters. Any acceptable number can be entered into the computer in either standard or scientific notation. The form in which Visual Basic displays a number depends on many factors, with size being an important consideration. In Visual Basic, b � 10 r is usually written as bEr. (The letter E is an abbreviation for exponent.) The following forms of the numbers just mentioned are equivalent. 1.4 * 10^9 1.4E+09 1 4E+9 1.4E9 1400000000 3 * 10^–7 3E–07 3E–7 .0000003 The computer displays r as a two-digit number, preceded by a plus sign if r is positive and a minus sign if r is negative. EXAMPLE 2 The following program illustrates scientific notation. The computer’s choice of whether to display a number in scientific or standard form depends on the magnitude of the number. Private Sub cmdCompute_Click() picResults.Cls picResults.Print 1.2 * 10 ^ 34 picResults.Print 1.2 * 10 ^ 8 picResults.Print 1.2 * 10 ^ 3 picResults.Print 10 ^ -20 picResults.Print 10 ^ -2 End Sub [Run and then click the command button.]
■ VARIABLES In applied mathematics problems, quantities are referred to by names. For instance, consider the following high school algebra problem. “If a car travels at 50 miles per hour, how far will it travel in 14 hours? Also, how many hours are required to travel 410 miles?” The solution to this problem uses the well-known formula distance = speed × time elapsed Here’s how this problem would be solved with a computer program. Private Sub cmdCompute_Click() picResults.Cls speed = 50 timeElapsed = 14 distance = speed * timeElapsed picResults.Print distance distance = 410 timeElapsed = distance / speed picResults.Print timeElapsed End Sub [Run, and then click the command button. The following is displayed in the picture box.] 700 8.2 The third line of the event procedure sets the speed to 50, and the fourth line sets the time elapsed to 14. The fifth line multiplies the value for the speed by the value for the time elapsed and sets the distance to this product. The next line displays the answer to the first question. The three lines before the End Sub statement answer the second question in a similar manner. The names speed, timeElapsed, and distance, which hold numbers, are referred to as variables. Consider the variable timeElapsed. In the fourth line, its value was set to 14. In the eighth line, its value was changed as the result of a computation. On the other hand, the variable speed had the same value, 50, throughout the program. In general, a variable is a name that is used to refer to an item of data. The value assigned to the variable may change during the execution of the program. In Visual Basic, variable names can be up to 255 characters long, must begin with a letter, and can consist only of letters, digits, and underscores. (The shortest variable names consist of a single letter.) Visual Basic does not distinguish between uppercase and lowercase letters used in variable names. Some examples of variable names are total, numberOfCars, taxRate_1999, and n. As a convention, we write variable names in lowercase letters except for the first letters of additional words (as in numberOfCars). If var is a variable and num is a constant, then the statement var = num assigns the number num to the variable var. (Such a statement is called an assignment statement.) Actually, the computer sets aside a location in memory with the name var and places the number num in it. The statement picBox.Print var Numbers 37
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Page 3 and 4: CONTENTS SECTION 1: PROBLEM SOLVING
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3. In Appendix D, the section “St
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Private Sub cmdDetermine_Click() Di
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Private Sub cmdCompute_Click() Dim
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preceded with the word ByVal. Built
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It is clear from the hierarchy char
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The meaningful procedure names, alo
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FIGURE 3-9 Sample Run for Programmi
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4.1 RELATIONAL AND LOGICAL OPERATOR
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(a) (2 < n) And (n < 6) (b) (2 < n)
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SOLUTION: In the following program,
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The Else part of an If block can be
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picTax.Cls picTax.Print “Your FIC
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Case 4, 5 picOutcome.Print “You a
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EXAMPLE 3 The following program use
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Case Else picResult.Print “The st
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4. The items in the value list must
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The hierarchy chart in Figure 4-4 s
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‘Program to compute employees’
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Private Function TaxMarried(adjPay
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and tells us whether the food meets
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S E C T I O N 5 REPETITION
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132 Computer Programming Concepts a
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S E C T I O N 6 ARRAYS
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S E C T I O N 7 SEQUENTIAL FILES
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S E C T I O N 8 RANDOM-ACCESS FILES
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S E C T I O N 9 THE GRAPHICAL DISPL
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10.1 LIST BOXES AND COMBO BOXES The
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Private Sub cmdAdd_Click() Dim item
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either typing in information or jus
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Private Sub cmdDisplay_Click() picF
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clicks on the square to toggle betw
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circle and the button is said to be
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hsbBar.Value changes accordingly. T
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THE SHAPE CONTROL The shape control
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FIGURE 10-9 A Picture Created with
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Rows 9 ScrollBars 0 - flexScrollBar
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Private Sub cmdQuit_Click() End End
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Here, the menu bar contains two men
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Clipboard.Clear deletes the content
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cedures that are available to all f
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The Flags property influences certa
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13. Additional forms serve as new w
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6. Voting Machine. The members of t
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11.1 AN INTRODUCTION TO DATABASES T
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9. Click on the down arrow to the r
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clicked or a Move, Update, Delete,
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Do While (Not foundFlag) And (Not d
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mary key. Databases of student enro
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question mark stands for a single c
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1995 populations. When the second c
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If a Find method does not locate a
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place an x in the check box next to
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population (in descending order). W
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Creating and Designing Databases 34
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9. When all fields have been specif
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Creating and Designing Databases 34
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TABLE 11.5(B) TABLE 11.5(C) course
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(a) Update the quantity field of th
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12.1 CLASSES AND OBJECTS noun A wor
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Task Statement Assign a value to a
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EXAMPLE 1 and then an instance of t
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[Run, enter the data for a student
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SOLUTION: Object Property Setting f
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4. Methods can be either Function o
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‘Student Class (CStudent) Private
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txtFinal.Text = “” picGrades.Pr
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■ EVENTS In the previous section
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frmCircles.ForeColor = vbRed ‘Mak
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Public Function X() As Integer X =
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End Sub Private Sub cmdDropBomb_Cli
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Next i End Sub Public Function Read
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Remove method. The number of object
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S E C T I O N 13 COMMUNICATING WITH
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A P P E N D I C E S
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APPENDIX C VISUAL BASIC STATEMENTS,
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CANCEL The Cancel property provides
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COLS and ROWS The Cols and Rows pro
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DEFINT, DEFLNG, DEFSNG, DEFDBL, DEF
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ENVIRON Visual Basic has an environ
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FONT.ITALIC or FONTITALIC These pro
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yields “1234.”, Format(1234000,
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the length of the string currently
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ISNUMERIC The value of the function
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Unlock statement is used to remove
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Focus Default Default Number First
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OR (Logical Operator) The logical e
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the same as in the original Dimensi
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SECOND The function Second extracts
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STRETCH When the Stretch property o
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UNLOCK The Unlock command is intend
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[COLOR]: Numbers written in base 16
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Appendix D 457
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466 Technology of the Internet D Da
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468 Technology of the Internet Rela
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470 Technology of the Internet 2. D
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SYSTEM REQUIREMENTS CD-ROM INSTRUCT
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Computer Programming Concepts and Visual Basic David I. Schneider

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