microsoft visual basic 2010: reloaded fourth edition chapter ten string manipulation and menus

Microsoft Visual Basic 2010: Reloaded Fourth Edition

Chapter TenString Manipulation and Menus

Objectives

After studying this chapter, you should be able to:

• Determine the number of characters in a string

• Remove characters from a string

• Insert characters in a string

• Search a string

• Access the characters in a string

Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Objectives (cont’d.)

• Align the characters in a string

• Compare strings using pattern-matching

• Add a menu to a form

• Code a menu item’s Click event procedure


Working with Strings

• Most applications need to manipulate string data in some way

• String properties and methods are used to manipulate string data

Microsoft Visual Basic 2010: Reloaded, Fourth Edition 4

Determining the Number of Characters in a String

• Length property: stores the number of characters contained in a string as an integer value– Can be used with a String variable, a String named

constant, or the Text property of a control



Figure 10-1: How to determine the number of characters in a string6

Removing Characters from a String

• Computer first makes a temporary copy of the string in memory and operates on the copy only

• Trim method: removes one or more spaces from both the beginning and end of a string

• Remove method: removes a specified number of characters located anywhere in a string

• Index: an integer indicating the character’s position in the string– The first character in a string has an index of 0


Removing Characters from a String (cont’d.)

• Arguments:– startIndex argument: the index of the first character

to be removed– numCharsToRemove argument: number of

characters to be removed• If omitted, all characters from the startIndex position

through the end of the string are removed



Figure 10-2: How to remove characters from a string

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Figure 10-2: How to remove characters from a string (cont’d.)

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Inserting Characters in a String

• Insert method: used to insert characters anywhere within a string

• Computer makes and operates on a temporary copy of the string

• Arguments:– startIndex: specifies where in the string to insert the

value– value: the character(s) to be inserted

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Figure 10-3: How to insert characters in a string

Inserting Characters in a String (cont’d.)

Searching a String

• Contains method: – Determines if a string contains a specific sequence

of characters– Returns a Boolean value of True when the substring

is contained in the string, and False if not– Performs a case-sensitive search

• Arguments:– subString: represents the sequence of characters to

be searched for


Searching a String (cont’d.)

• IndexOf method: returns an integer representing the location of a substring within a string – Performs a case-sensitive search

• Arguments:– subString: sequence of characters to be searched

for– startIndex: the starting position for the search (zero-

relative)



Figure 10-4: How to search a string


Figure 10-4: How to search a string (cont’d.)


Accessing the Characters in a String

• Substring method: accesses any number of characters contained in a string

• Arguments:– startIndex: index of the first character to be

accessed (zero-relative)– numCharsToAccess: number of characters to be

accessed

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Figure 10-5: How to access characters in a string

Accessing the Characters in a String (cont’d.)

Aligning the Characters in a String

• PadLeft method: inserts characters at the beginning of a string

• PadRight method: inserts characters at the end of a string

• Arguments:– totalChars: represents the total number of characters

you want in the resulting string– padCharacter: the character used to pad the string;

default value is the space character



Figure 10-6: How to align the characters in a string

Using Pattern-Matching to Compare Strings

• Like operator: – Uses pattern-matching characters to determine if

one string is equal to another– Returns a Boolean value (True/False)

• Arguments:– pattern: contains one or more pattern-matching

characters– characterList: a listing of characters to be matched


Using Pattern-Matching to Compare Strings

• Pattern-matching characters:– ? Represents 1 character only– * represents 0 or more characters– # represents a single digit

• Use square brackets [ ] to provide a list of characters to match– Use a hyphen between characters to specify a range

of characters



Figure 10-7: How to use pattern-matching to compare strings


Figure 10-7: How to use pattern-matching to compare strings (cont'd.)

Adding a Menu to a Form

• Menu strip control: used to include one or more menus on a Windows form– Found in the Menus & Toolbars section of the

toolbox

• Menu title: appears on the menu bar at the top of the form– When clicked, the menu opens and displays a list of

options called menu items

• Clicking a menu item executes the command associated with it


Adding a Menu to a Form (cont’d.)


Figure 10-8: Location of menu elements

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• Each menu element is considered an object– Each has a set of properties associated with it

• Name property: used to refer to the menu element in code

• Text property: stores the menu element’s caption – the text the user sees

• Access key: used in combination with the Alt key, will open the menu

• Shortcut key: allows the user to select the item without opening the menu




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Figure 10-9: Game menu

Figure 10-10: Exit command’s Click event procedure

• Creating the Guess the Word Game Application


Programming Tutorial 1

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Figure 10-12: MainForm in the Guess the Word Game application

• Creating the Bucky Burgers Application


Programming Tutorial 2

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Figure 10-22: MainForm for the Bucky Burgers application


Programming Example

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• Yolanda Drapery Application

Figure 10-28: MainForm in the Yolanda Drapery application


Summary

• Use a menu strip control to add one or more menus to a form

• Menu elements should have access keys

• String manipulation techniques:– Length property: number of characters in the string– Trim method: removes leading and trailing spaces– Remove method: removes characters from a string– Insert method: inserts characters into a string

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Summary (cont'd.)

• String manipulation techniques (cont’d.):– Contains method: determines whether a specific

sequence of characters appears in a string; returns a Boolean value

– IndexOf method: determines whether a specific sequence of characters appears in a string; returns the integer position where the sequence starts

– Substring method: accesses one or more characters in a string

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Summary (cont'd.)

• String manipulation techniques (cont’d.):– PadLeft method: pads the beginning of a string with

the specified character– PadRight method: pads the end of a string with the

specified character– Like operator: uses pattern-matching to compare

strings

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