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Objectives

• Determine the number of characters contained in a
  string
• Remove characters from a string
• Determine whether a string begins or ends with
  one or more specific characters
• Access characters in a string
• Insert characters in a string
• Search a string for one or more characters
• Compare strings using the Like operator

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Manipulating Stings in Visual Basic .NET

• Applications often need to manipulate (process)
  strings
• Verify part number begins with a specific letter
• Determine whether last 3 characters of employee
  number are valid
• Start by determining number of characters
  contained in a string

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Determining the Number of Characters Contained in
a String
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Removing Characters from a String
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The Remove Method

• Removes characters from anywhere in the string
• Uses characters index which indicates a
  characters position in string
• startIndex, count determine starting position
  and number of characters to remove respectively
• startIndex is zero based? to remove the first
  character, it must have a value of 0

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HOW TO
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Determining Whether a String Begins or Ends with
a Specific Sequence of Characters

• Use StartsWith method to determine whether a
  specific sequence of characters (substring)
  occurs at beginning of string
• Returns true if substring at beginning, false
  otherwise
• Use EndsWith method to determine whether a
  specific sequence of characters (substring)
  occurs at ending of string
• Returns true if substring at ending, false
  otherwise

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HOW TO
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HOW TO(continued)
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Accessing Characters Contained in a String

• Use Substring method
• Method has two arguments
• startIndex argument refers to index of the first
  character you want to access
• count argument refers to number of characters to
  access
• count argument is optional

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HOW TO
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Replacing Characters in a String

• Use Replace method
• Replaces a sequence of characters with another
  sequence of characters
• Contains two arguments
• oldValue argument is the sequence to be removed
• newValue argument is the sequence of characters
  to be inserted
• Replaces all occurrences of oldValue with
  newValue in the string

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HOW TO
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Mid Statement

• Replaces a specified number of characters in a
  string with characters from another string
• targetString - string in which you want
  characters replaced
• start - character position of the first character
  you want replaced
• count - specifies the number of characters to
  replace and is optional
• replacementString - contains the replacement
  characters

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HOW TO
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Inserting Characters at the Beginning and End of
a String

• PadLeft method pads string on the left,
  inserting characters at the beginning
• PadRight method pads string on the right,
  inserting characters at the end of the string
• length argument is the desired length of the
  string (total number of characters including
  inserted characters)
• character argument is optional and specifies the
  character you want to pad with
• If blank, the space character is used

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HOW TO
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Inserting Characters within a String

• Insert Method inserts a character or characters
  in a string at a specified location
• startIndex argument specifies where you want the
  value to be inserted
• value argument is the character of characters you
  want to insert

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HOW TO
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Searching a String

• IndexOf method searches a string for a specific
  sequence of characters and returns the beginning
  position if found or a -1 if not found
• value argument - specific sequence to search for
• startIndex argument is optional and is the
  starting position to begin search

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HOW TO
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The Like Operator

• Uses pattern-matching characters to determine
  whether one string is equal to another string
• Pattern-matching characters specify zero or more
  characters that fit a specific pattern or
  character type
• You can specify a charlist which is a list of
  characters that can occur in the pattern
• Use Like operator in an expression to return true
  if a match occurs, false otherwise

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HOW TO
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Summary of String Manipulation
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Programming Example Hangmans Game

• Application simulates a simplified version of the
  Hangman game with the following rules
• Words have 5 letters
• Word is initially represented by 5 dashes
• An attempt is made to guess a letter and, if
  correct, the dash is replaced with the letter
• When all dashes have been replaced, the game is
  over or, when 10 incorrect guesses have occurred
  (whichever occurs first)

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TOE Chart
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User Interface
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Objects, Properties, and Settings
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Tab Order
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Psuedocode

• btnExit Click event procedure
• close the application
• btnPlay Click event procedure
• get a 5-letter word from player 1
• repeat while the word does not contain 5 letters
• get a 5-letter word from the user
• end repeat
• convert word to upper case
• display five dashes in the lblWord control
• clear the lblIncorrectGuesses control
• repeat while the came is not over
• get a letter from player 2, convert the letter
  to uppercase
• (continued on next slide)

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Psuedocode (continued)

• repeat for each character in the word
• if the current character is equal to the letter
  entered by player 2
• replace the appropriate dash in the lblWord
  control
• set the blnDashReplaced variable to true
• end if
• end repeat
• If a dash was replaced in the lblWord control
• if the lblWord control does not contain any
  dashes
• set the blnGameOver variable to True
• display the Great Guessing! message in a
  message box
• else
• reset the blnDashReplaced variable to False
• end if
• (continued on next slide)

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Psuedocode (continued)

• else
• add 1 to the intIncorrectGuesses counter
  variable
• display the intIncorrectGuesses value in
  lblIncorrectGuesses
• if the user made 10 incorrect guesses
• set the blnGameOver variable to True
• display the Game Over message in lblWord
  control
• display the Sorry, the word is message and
  the word in a message box
• end if
• endif
• end repeat

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Code
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Code (continued)
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Summary

• Use the Length property to determine number of
  characters in a string
• TrimStart and TrimEnd methods respectively
  removes characters from beginning or end of
  strings
• Use Remove method to remove characters anywhere
  in the string
• StartsWith method determines whether a string
  begins with a specific sequence of characters

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Summary (continued)

• EndsWith method determines whether a string ends
  with a specific sequence of characters
• Substring method accesses one or more characters
  contained in a string
• Replace method replaces all occurrences of a
  given sequence of characters with another
  sequence of characters
• Mid statement replaces a specific number of
  characters with characters from another string

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Summary (continued)

• PadLeft allows (padding) insertion of characters
  at beginning of string.
• PadRight allows (padding) insertion of characters
  at end of string
• Insert method inserts characters within a string
  and returns string with characters inserted
• IndexOf method searches for a specific sequence
  of characters and returns the index of the
  starting character in the sequence or a 1 if
  not found

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Summary (continued)

• Like comparison operator allows you to use
  pattern-matching characters to determine whether
  one string is equal to another string