Chapter 8: Manipulating Strings

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Chapter 8 Manipulating Strings
Programming with Microsoft Visual Basic 2005,
Third Edition
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String ManipulationLesson A Objectives

• Determine the number of characters contained in a
  string
• Remove characters from a string
• Replace one or more characters in a string
• Insert characters within a string

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String ManipulationLesson A Objectives
(continued)

• Search a string for one or more characters
• Access characters contained in a string
• Compare strings

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Manipulating Strings in Visual Basic 2005

• Applications often need to manipulate string data
• Two scenarios involving string manipulation
• Determining the first letter of an inventory part
  id
• Validating last three characters in an employee
  id

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Determining the Number of Characters Contained in
a String

• Length property
• Stores number of characters contained in a string
• Syntax of the Length property string.Length
• Using Length property to validate length of ZIP
  code
• Dim numChars As Integer numChars
  Me.xZipTextBox.Text.Length
• Length of entered ZIP code is assigned to
  numChars

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Removing Characters from a String

• TrimStart method
• Removes one or more characters from start of
  string
• TrimEnd method
• Removes one or more characters from end of string
• Trim method
• Removes one or more characters from both ends
• All methods take optional trimChars argument

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Removing Characters from a String (continued)
Figure 8-4 Syntax, purpose, and examples of the
TrimStart, TrimEnd, and Trim methods (continued)
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Removing Characters from a String (continued)
Figure 8-4 Syntax, purpose, and examples of the
TrimStart, TrimEnd, and Trim methods
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The Remove Method

• Remove method
• Removes one or more characters anywhere in string
• Returns a string with appropriate characters
  removed
• Syntax string.Remove(startIndex, count)
• Example
• Dim fullName As String "John Cober
  Me.xNameTextBox.Text fullName.Remove(0, 5)
• Assigns Cober to xNameTextBoxs Text property

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Replacing Characters in a String

• Replace method
• Replace one sequence of characters with another
• Example replace area code 800 with 877
• Replace syntax string.Replace(oldValue,
  newValue)
• oldValue sequence of characters in string to
  replace
• newValue the replacement characters
• Replace method returns a string with newValue

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Replacing Characters in a String (continued)
Figure 8-6 Syntax, purpose, and examples of the
Replace method
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The Mid Statement

• Mid statement
• Replaces set of characters with another string
• Syntax Mid(targetString, start , count)
  
  
  replacementString
• targetString string targeted for character
  replacement
• replacementString contains replacement
  characters
• start position of first character of the
  targetString
• count number of characters to replace in
  targetString

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The Mid Statement (continued)
Figure 8-7 Syntax, purpose, and examples of the
Mid statement
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Inserting Characters at the Beginning and End of
a String

• PadLeft method
• Inserts padded characters at start of string
• Right-aligns the characters within the string
• Syntax string.PadLeft(length, character)
• PadRight method
• Inserts padded characters at the end of the
  string
• Left-aligns the characters within the string
• Syntax string.PadRight(length, character)

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The Insert Method

• Insert method
• Inserts characters anywhere within a string
• Example insert middle initial within employee
  name
• Syntax string.Insert(startIndex, value)
• startIndex specifies position in string where
  value will be inserted

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The Insert Method (continued)
Figure 8-9 Syntax, purpose, and examples of the
Insert method
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Searching a String

• StartsWith method
• Determine if sequence occurs at start of string
• Syntax string.StartsWith(subString)
• EndsWith method
• Determine if sequence occurs at the end of a
  string
• Syntax string.EndsWith(subString)
• Both methods return Boolean value (True or False)

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The Contains Method

• Contains method
• Determines if string contains a character
  sequence
• Returns a Boolean value (True or False)
• Contains syntax string.Contains(subString)
• subString is the sequence to search for in string
  
• Example
• Dim phone As String "(312) 9999999
  If phone.Contains("(312)") Then
• Condition will evaluate to True

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The IndexOf Method

• IndexOf method
• Determine if string contains a character sequence
  
• Returns integer specifying start position of
  substring
• If substring is not found, method returns -1
• Syntax string.IndexOf(value, startIndex)
• value sequence of characters to search in the
  string
• startIndex index of character at which search
  begins

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The IndexOf Method (continued)
Figure 8-12 Syntax, purpose, and examples of the
IndexOf method (continued)
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The IndexOf Method (continued)
Figure 8-12 Syntax, purpose, and examples of the
IndexOf method
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Accessing Characters Contained in a String

• Substring method
• Used to access any number of characters in a
  string
• Returns string with specified number of
  characters
• Syntax string.Substring(startIndex, count)
• startIndex index of first character to access in
  string
• count specifies number of characters to access

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Accessing Characters Contained in a String
(continued)
Figure 8-13 Syntax, purpose, and examples of the
Substring method
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Comparing Strings

• String.Compare method
• Used to compare two strings
• Supplements the comparison operators
• Returns three values 1, 0, and -1
• Syntax String.Compare(string1,string2,ignoreCase
  )
• string1 and string2 are two strings to compare
• ignoreCase Boolean argument set to True or False
• Word sort rules are used to compare strings
• Numbers lt lowercase letters lt uppercase letters

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Comparing Strings (continued)
Figure 8-14 Syntax, purpose, and examples of the
String.Compare method
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Summary Lesson A

• Determine string length with Length property
• Methods for removing characters Trim, TrimStart,
  TrimEnd, and Remove
• Replace characters with Replace method and Mid
  statement
• Pad strings with PadLeft and PadRight methods
• Insert characters in a string with the Insert
  method

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Summary Lesson A (continued)

• Methods determining presence of a substring
  StartsWith, EndsWith, Contains, and IndexOf
• Access one or more characters in a string using
  the Substring method
• Compare strings using String.Compare method, Like
  operator, or comparison operators

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Adding a Menu to a FormLesson B Objectives

• Include a MenuStrip control on a form
• Add elements to a menu
• Assign access keys to menu elements
• Assign shortcut keys to commonly used menu items
• Code a menu items Click event procedure

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Completing the Hangman Game Applications User
Interface

• Objective create simplified version of Hangman
• Lesson tasks
• Complete the applications user interface
• Begin coding the application

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Completing the Hangman Game Applications User
Interface (continued)
Figure 8-16 Partially completed interface for
the Hangman Game application
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Creating Menus

• MenuStrip control basis for adding menus
• MenuStrip tool instantiates MenuStrip control
• Menu title appears on menu bar at top of form
• Menu items
• Commands, submenu items, or separator bars
• Clicking a command on the menu executes it
• Clicking a submenu item opens an additional menu

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Creating Menus (continued)
Figure 8-17 Location of menu elements
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Creating Menus (continued)

• Menu title captions should be one word only
• Menu item captions can be from one to three words
• Assign unique access keys to menu titles and
  items
• Follow Windows menu conventions
• Ellipsis () after item caption indicates need
  for input
• File menu should be first menu on menu bar
• Cut, Copy, Paste should appear on an Edit menu

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Assigning Shortcut Keys to Menu Items

• Shortcut keys
• Appear to the right of a menu item
• Allow you to select an item without opening a
  menu
• Example Ctrl S executes Save in MS Word
• Assign shortcut keys to commonly used menu items

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Assigning Shortcut Keys (continued)
Figure 8-23 Shortcut key appears next to the New
Game menu item
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Coding the Exit Options Click Event Procedure

• How to end the Hangman Game application
• User clicks the Exit item on the File menu
• Exit items Click event procedure calls Me.close()

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Summary Lesson B

• MenuStrip control is the basis for a menu
• Menu items commands, submenu items, separator
  bars
• Assign a unique access key to each menu element
• Assign shortcut keys to commonly used menu items
• Follow the Windows standard when creating menus

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Completing the Hangman Game ApplicationLesson C
Objectives

• Include the Length property in a procedure
• Include the Substring method in a procedure
• Include the Mid statement in a procedure
• Include the Contains method in a procedure

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The Hangman Game Application

• Application requirements
• Allow one student to enter a five-letter word
• Allow another student to guess word, letter by
  letter
• Two events can end the game
• Second student guesses all of the letters in the
  word
• Second student makes 10 incorrect guesses

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Coding the xFileNewMenuItems Click Event
Procedure

• Two ways to begin a new Hangman game
• Click File on the menu bar, then click New Game
• Press Ctrl N

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Coding the xFileNewMenuItems Click Event
Procedure (continued)
Figure 8-26 Pseudocode for the
xFileNewMenuItems Click event procedure
(continued)
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Coding the xFileNewMenuItems Click Event
Procedure (continued)
Figure 8-26 Pseudocode for the
xFileNewMenuItems Click event procedure
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Coding the xFileNewMenuItems Click Event
Procedure (continued)
Figure 8-33 Result of guessing the word
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Summary Lesson C

• Hangman application uses various methods to
  manipulate strings
• Substring method used to access characters in a
  string
• Mid statement replaces one character with
  another
• Contains method determines whether a specific
  character is within a string