Mgmt 362a Interest Calculator Application

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11

• Mgmt 362a Interest CalculatorApplication
• Introducing the For...NextRepetition Statement

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Objectives

• In this tutorial you will learn
• Execute statements repeatedly with the For...Next
  repetition statement.
• Obtain user input with the NumericUpDown control.
• Display information, using a multiline TextBox.
• Use type String.

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11.1 Test-Driving the Interest Calculator
Application

• You are considering investing 1,000.00 in a
  savings account that yields 5 interest, and you
  want to forecast how your investment will grow.
  Assuming that you will leave all interest on
  deposit, calculate and print the amount of money
  in the account at the end of each year over a
  period of n years. To compute these amounts, use
  the following formula
• a p (1 r)n
• where
• p is the original amount of money invested
  (the principal) r is the annual interest rate
  (for example, .05 is equivalent to 5) n is the
  number of years a is the amount on deposit at
  the end of the nth year.

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11.1 Test-Driving the Interest Calculator
Application (Cont.)

• Figure 11.1 Completed Interest Calculator
  application.

• Executing the application

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11.1 Test-Driving the Interest Calculator
Application (Cont.)

• Enter data into application
• Principal and interest rate entered
• Using NumericUpDown control to increase years
• Program output
• Output displayed in multiline TextBox
• Vertical scrollbar enabled

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11.1 Test-Driving the Interest Calculator
Application (Cont.)

• Figure 11.2 Output of completed Interest
  Calculator application.

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11.2 Essentials of Counter-Controlled Repetition

• Four essential elements of counter-controlled
  repetition
• The name of a control variable (or loop counter)
  that is used to determine the whether the loop
  continues to iterate
• The initial value of a control variable
• The increment (or decrement) by which the control
  variable is modified after each iteration
• The condition that tests for the final value of
  the control variable

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Outline
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11.3 Introducing the For...Next Repetition
Statement

• Figure 11.4 For...Next header components.

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Good Programming Practice

• Place a blank line before and after each control
  statement to make it stand out in the code.

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Error-Prevention Tip

• Although the value of the control variable can be
  changed in the body of a For...Next loop,avoid
  doing so, because this practice canlead to
  subtle errors.

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Good Programming Practice

• Vertical spacing above and below
  controlstatements, as well as indentation of the
  bodiesof control statements, enhances
  readability.

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Error-Prevention Tip

• If you use a For...Next loop for
  counter-controlled repetition, off-by-one errors
  (which occur when a loop is executed for one more
  or one fewer iteration than is necessary) are
  normally avoided, because the terminating value
  is clear.

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Common Programming Error

• Counter-controlled loops should not be
  controlledwith floating-point variables. These
  are represented only approximately in the
  computers memory, possibly resulting in
  imprecise counter valuesand inaccurate tests for
  termination that couldlead to logic errors.

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Outline
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11.5 Adding and Customizing a NumericUpDown
Control

• Figure 11.8 Template Interest Calculator
  application Form in design view.

• Template Form in Design view
• Adding NumericUpDown control
• Adding a multiline TextBox

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11.5 Adding and Customizing a NumericUpDown
Control (Cont.)

• NumericUpDown control
• Increment property
• Increment property default value
• ReadOnly property
• Range Limits
• Maximum property
• Minimum property

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GUI Design Tip

• A NumericUpDown control should follow the same
  GUI Design Guidelines as a TextBox. (See
  Appendix C.)

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11.5 Adding and Customizing a NumericUpDown
Control (Cont.)

• Figure 11.9 NumericUpDown control added to
  Interest Calculator application.

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Good Programming Practice

• Append the UpDown suffix to NumericUpDowncontrol
  names.

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GUI Design Tip

• Use a NumericUpDown control to limitthe range of
  user input.

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11.5 Adding and Customizing a MultilineTextBox
with a Scrollbar

• Multiline TextBox
• Can use scrollbar
• Enable vertical scrollbar

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GUI Design Tip

• If a TextBox will display multiple lines of
  output,set the Multiline property to True and
  left align the output by setting the TextAlign
  property to Left.

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GUI Design Tip

• If a multiline TextBox will display many lines
  ofoutput, limit the TextBox height and use a
  vertical scrollbar to allow users to view
  additional linesof output.

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11.5 Adding and Customizing a MultilineTextBox
with a Scrollbar (Cont.)

• Figure 11.10 Multiline TextBox with vertical
  scrollbar added to the Form.

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11.5 Adding a Click Event Handler

• Declaring variables
• Declaring a counter variable
• Retrieving user input
• Storing user input into variables

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11.5 Adding a Click Event Handler (Cont.)

• Figure 11.11 Application code for retrieving
  and storing user input.

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11.5 Adding a Click Event Handler (Cont.)

• Figure 11.12 Application code for displaying a
  header in a multiline TextBox.

• Displaying header text in multiline TextBox
• Using ControlChars.Tab
• Using ControlChars.CrLf

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11.5 Calculating Cumulative Interest with
aFor...Next Statement

• Figure 11.13 Application code for For...Next
  statement.

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11.5 Calculating Cumulative Interest with
aFor...Next Statement (Cont.)

• Figure 11.14 Application code for displaying
  calculation results.

• Displaying results in a multiline TextBox

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Outline
(1 of 2 )
Declare a variable of type String
Use the Value property of yearUpdDown
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Outline
Construct a header for the TextBox as a String
(2 of 2 )
Loop from 1 to year
Append result of calculation to the String named
output
Display results in resultTextBox