1. Data Types and Variables Part D – Common Methods (ToString and Parse)
Lecture Set 4
Data Types and Variables
Part D – Common Methods (ToString and Parse)
Text Boxes, Input Focus

2. Objectives Learn about two Common Methods for converting
To a formatted string (Tostring) from a primitive (or other) value
From a string to a primitive value (Parse)
Examine Imports
Future Value
Learn how to use the TextBox control
Define the order in which control instances get input focus
11/10/2018 7:35 PM

3. Formatting Output Strings
There are a number of common functions that can be used to convert and format data.
These include the ToString method, which converts an argument to a string which can be specially formatted
Also, a Parse method which converts a string to an equivalent data value
Visual Studio supports named formats to supply common formatting -- currency, for example
Data can be formatted with format specifiers
Custom formats can be created with placeholder characters
11/10/2018 7:35 PM

4. The ToString and Parse Methods
Both are conversion methods common to all data types defined by .NET
So we can write
… Decimal.Parse (“ D”);
… DateTime.Parse (“Jan 30, 2007”);
How does the compiler know which version of these functions to use?
What would happen if we wrote
… Decimal.Parse (“Jan 30, 2007”);
11/10/2018 7:35 PM

5. Formatting Data Using ToString
Here we see another version of the ToString method
Previously we had seen a version of ToString that took a primitive type value as an argument
Now we have a version of the Common Method ToString that takes a format descriptor (or no argument)
With the format descriptor, the specified value to converted to a formatted string
A format specifier consists of a single alphabetic character followed by an optional numeric precision indicator 
11/10/2018 7:35 PM

6. Format Descriptors Format descriptors may be
Specifier strings consisting of a single alphabetic character followed by an optional numeric precision specifier
A format string or mask consisting of special placeholder characters and literal characters
value.ToString(“C”);
value.ToString (“D6”);
value.ToString(“$###,###.00”);
Examples next … 
11/10/2018 7:35 PM

7. Format Specifiers
11/10/2018 7:35 PM

8. Placeholder Characters
11/10/2018 7:35 PM

9. Format Strings (Examples)
11/10/2018 7:35 PM

10. The FV Function
The FV function calculates the future value of an investment (like do we really have any?)
The first argument contains the interest rate
The second argument contains the number of periods
The third argument contains the amount of the periodic payment
The optional fourth argument contains the present (initial) value of the investment
The optional fifth argument defines whether payments are made at the beginning or end of the period
Slide 11
11/10/2018 7:35 PM

11. The FV Function (Example) 1
Calculate the future value of $1, for 12 periods at 1% per period
double monthRate = 0.01;
int monthTerm = 12;
double initialValue = ;
double futureValue;
futureValue = FV(0.01, 12, 0, 1000);
futureValue = FV (monthRate,
monthTerm, 0, initialValue);

12. The FV Function (Example) 2
But the FV functions returns a negative value
So what do we do?
Using System.Convert; ‘Why?
InitialValue = ToDouble(txtInitialValue.Text);
AnnualInterestRate = … ;
YearlyTerm = ToInt32(txtYearlyTerm.Text);
MonthlyTerm = …
FutureValue = FV(…)
FutureValue = System.Math.Abs(FutureValue);
// Convert to string in currency format and store in box
// Note different ways to call operators such as toString
lblFutureValue.Text = FutureValue.ToString(“C”);
11/10/2018 7:35 PM

13. The TextBox Control (Introduction)
The TextBox control gets input and displays output
The control derives from the TextBoxBase class
Other textual controls include the MaskedTextBox and RichTextBox controls
11/10/2018 7:35 PM

14. The TextBox Control (Properties) 1
The BorderStyle property defines the style of the border
The ForeColor and BackColor properties define text and background colors
The Enabled property defines whether the control instance can get input focus
The ReadOnly property controls whether the text in the control instance can be copied to the clipboard
The MultiLine property defines whether text will appear on multiple lines
The maximum number of characters is defined in the MaxLength property
11/10/2018 7:35 PM

15. The TextBox Control (Properties) 2
The ScrollBars property defines whether scroll bars appear
Scroll bars only appear when the MultiLine property is True
The Text property stores the visible text
The TextAlign property defines how the text is aligned in the control instance
The size and position is defined by the X, Y, Height, and Width properties
11/10/2018 7:35 PM

16. The TextBox Control (Methods and Events)
The Focus method is used to set input focus to a text box
The Enter event fires when the control instance gets focus
The Leave event fires when the control instance loses focus
11/10/2018 7:35 PM

17. Introduction to Tab Order
Every form has exactly one active control instance at run time
This is the control instance having input focus
The order in which control instances get focus is called the tab order
The tab order is set using the TabIndex property
The tab order can also be set using a visual designer
11/10/2018 7:35 PM

18. Setting the Tab Order
11/10/2018 7:35 PM

19. Other Issues (optional)
Read about enumerations – nothing new here
Nullable types – can be used to indicate that a variable has never been defined – in other words that the value is unknown
Used only for value variables
Int? myVariable = null; // null is a keyword
You should never depend on a language system to initialize data for you. Do it yourself explicitly
If you do this carefully you will probably not need to use nullable types
NOTE: Reference variables are by default assigned the null value
11/10/2018 7:35 PM