string manipulation chapter microsoft visual basic.net: reloaded 1

String Manipulation

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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 character’s 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…(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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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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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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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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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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Summary of String Manipulation

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Programming Example – Hangman’s 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 wordif the current character is equal to the letter entered by player 2

replace the appropriate dash in the lblWord controlset the blnDashReplaced variable to true

end ifend repeatIf a dash was replaced in the lblWord control

if the lblWord control does not contain any dashesset the blnGameOver variable to Truedisplay the “Great Guessing!” message in a message box

elsereset 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