csci 3327 visual basic chapter 12: strings, characters and regular expressions utpa – fall 2011

CSCI 3327 Visual Basic CSCI 3327 Visual Basic Chapter 12: Strings, Characters Chapter 12: Strings, Characters

and Regular Expressionsand Regular Expressions

UTPA – Fall 2011

Objectives

• In this chapter, you will– Learn how to create and manipulate String objects– Get familiar with common methods of String class– Learn how to create and manipulate StringBuilder

objects– Know how to use regular expressions in

conjunction with classes Regex and Match– Learn how to search for patterns in text using

regular expressions

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Online Chapters

• URL:– www.pearsonhighered.com/deitel/– Chapter 17 - Download: PDF

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Strings

• A string is a series of characters treated as a single unit– Characters:

• uppercase/lowercase letters

• digits

• special characters (e.g. +, -, *, /, $ etc.)

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Characters

• A character literal is a character that is represented internally as an integer value, called a character code– ASCII code:

• "a" 97• "z" 122• """ 34

– In Visual Basic, letter c following the closing double quote is the syntax for character literal

• "a"c• ","c -- parameter of the Split function

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String Constructors

• Dim string0 As String = “hello”• Dim string1 As String = string0• Dim string2 As New String(characterArray)• Dim string3 As New String(characterArray, 6, 3)• Dim string4 As New String("?", 5)

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Example 17.1: StringConstructor.vb

• URL:– http://media.pearsoncmg.com/ph/esm/deitel/vb_ht

p_2010/codeexamples.html

• Constructors– Function Chr(34) – output double-quote (")

character– Console.WriteLine("The word ""four"" contains 4

characters")• Output: The word "four" contains 4 characters

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http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/codeexamples.html


String Indexer and Length Property

• Dim string1 As String = "Hello there!"

• Length property– string1.Length

• String indexer – string1(i)– i is index from 0 to string1.Length-1

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CopyTo Method of String

• Dim string1 As String = "Hello there!"• Dim characterArray() As Char = New Char (5) {}• CopyTo method

– string1.CopyTo(0, characterArray, 0, 5)• First argument: beginning position of copying characters in the

string1

• Second argument: character array into which characters are copied

• Third argument: starting position to copy to in character array

• Fourth argument: the number of characters to be copied from string1

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Example 17.2: StringMethod.vb

• URL:– http://media.pearsoncmg.com/ph/esm/deitel/vb_ht

p_2010/codeexamples.html

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Comparing Strings

• string1.Equals(“hello”)• string1 = “hello”• String.Equals(string1, string2)• string1.CompareTo(string2)

– If string1 < string2, -1– If string1 > string2, 1– If string1 = string2, 0

• Note: Nothing is a Null reference, and cannot be compared with an empty string (String.Empty or "")

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Example 17.3: StringCompare.vb

• URL:– http://media.pearsoncmg.com/ph/esm/deitel/

vb_htp_2010/codeexamples.html

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Example 17.4: StringStartEnd.vb



• element.StartWith("st")

• element.EndWith("ed")

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Example 17.5: StringIndexMethods



• letters.IndexOf("c"c)

• letters.LastIndexOf("c"c)

• letters.IndexOfAny(searchLetters)

• letters.LastIndexOfAny(searchLetters)

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Extracting Substrings From Strings

• string1.Substring(arg1)– arg1 – the starting index to copy from string1– If index is outside the bounds of string1, then an

ArgumentOutOfRangeException occurs

• string1.Substring(arg1, arg2)– arg1 – the starting index to copy from string1– arg1 – the length of substring to copy• Example 17.6 (Substring.vb):• http://media.pearsoncmg.com/ph/esm/deitel/vb_htp_2010/

codeexamples.html

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Example 17.7: Concatenating Strings



• string1 & string2

• String.Concat(string1, string2)

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Other Methods of Strings

• string1.Replace("e"c, "E"c)

• string1.ToLower()

• string1.ToUpper()

• string1.Trim()– Remove whitespaces at the beginning and end of a

String

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Example 17.8: StringMethods2.vb



• Replace

• ToLower

• ToUpper

• Trim

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String Class vs. StringBuilder Class

• String’s contents can never change– Operations that seem to concatenate Strings are in

fact creating new Strings

• StringBuilder class is different

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csci 3327 visual basic chapter 12: strings, characters and regular expressions utpa – fall 2011

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