ASP.NET Programming with C# and SQL Server First Edition Chapter 5 Manipulating Strings with C#

ASP.NET Programming with C# and SQL Server

First Edition

Chapter 5Manipulating Strings with C#

Objectives

In this chapter, you will:

• Manipulate strings

• Parse strings

• Work with regular expressions

ASP.NET Programming with C# and SQL Server, First Edition 2

Introduction to Manipulating Strings

• Form data is submitted as strings, so you must learn to deal with strings

• Regular expressions are used for matching and manipulating strings according to specified rules


Manipulating Strings

• String: text contained within double quotation marks– Can be used as literal values or can be assigned to

variables

• Parsing: the act of extracting characters or substrings from a larger string– A Web page document is one large text string that

includes formatting and other information that must be extracted

– Browser parses the formatting information from a Web page before displaying the page


Manipulating Strings (cont’d.)

• String class: contains methods and properties for manipulating strings

• System.Net.Mail namespace: contains classes for sending e-mail to an SMTP server

• Simple Mail Transfer Protocol (SMTP): a protocol used by most e-mail systems to send messages over the Internet

• Namespace: an abstract container that manages identifiers in a C# program– Used to uniquely identify two elements with the

same nameASP.NET Programming with C# and SQL Server, First Edition 5


• @import processing directive: used to make a namespace available for use in an ASP.NET Web page

• Example: <%@ Import Namespace=“System.Net.Mail” %>

• using keyword: used as a directive to import classes defined in other namespaces into the current class file



• MailMessage class: used to create an e-mail object containing sender, recipient, subject, and bodyMailMessage emailObject = new MailMessage();

• MailAddress class: used to identify the e-mail address and display name of the sender or recipientMailAddress from = new MailAddress (“[email protected]”, “myBiz Support Team”);

– Use Add() method to assign MailAddress objects to the To, CC, and Bcc properties, but not the From property



• ASP.NET Web Site Administration Tool: used to administer and configure a Web site– Configure SMTP settings to send e-mail

• Must instantiate an SmtpClient class object– Set UseDefaultCredentials to true– Use Send() method, passing the MailMessage

object


Counting Characters in a String

• Length property: String class property that returns the number of characters in a string

• IsNullOrEmpty() method: returns true if a string variable contains an empty string, false if the string has 1 or more characters


Using Special Characters

• Must use an escape sequence to include basic types of special characters within a literal string

• Examples: – \” includes double quotation marks in the string

• For other types of special characters, use Unicode or XHTML character entities

• Examples:– © is represented by ©– “Copyright” is represented by ©

• Can use escape sequence in form \xhhhh, where hhhh is the hexadecimal value for the Unicode value


Changing Case

• ToLower() method: converts a text string to lowercase

• ToUpper() method: converts a text string to uppercase

• Syntax: append the method to the string variable name

• Example: String myName;

Response.Write(“<p>” + myName.toUpper() + “</p>”);

• Original value of the variable is not changed


Trimming Strings

• Use trimming methods of the String class to remove spaces or characters from a text string


Table 5-1 Trimming methods of the String class

Trimming Strings (cont’d.)

• If no argument is included, the trimming methods will remove spaces

• Can specify which characters to remove

• Can pass a character array argument to the trimming methods to remove any character in the array from the text string


Padding Strings

• Use padding methods of the String class to add characters to the beginning or end of a string– Length argument: represents total length of string

after padding, not the number of characters to add


Table 5-2 Padding methods of the String class

Parsing Strings

• C# provides several methods for parsing strings

• You can find, extract, and replace individual characters or substrings


Finding and Extracting Characters and Substrings

• It is common to extract characters and substrings from strings– Example: extract the name portion of an e-mail

address

• C# has several methods for finding and extracting characters

• Contains() method: returns true if the specified text was found in the string

• StartsWith() method: determines whether the specified text appears at the beginning of the string


Finding and Extracting Characters and Substrings (cont’d.)

• EndsWith() method: determines whether the specified text appears at the end of the string

• Some string methods return a numeric position– Character positions in a string start at position 0

• IndexOf() method: returns the position of the first instance of the specified character(s) in the string– Returns -1 if the character is not found

– Can specify a starting position for finding a match

• LastIndexOf() method returns the position of the last occurrence of the specified character(s) in the string



• Substring() method: extracts text from a string starting at the specified position– Can specify the number of characters to be

extracted

• Chars property: retrieves a character by its specified index in a text string– Do not actually refer to it in your code– Use brackets enclosing the index position

– Example: myString[6]



Table 5-3 Search and extraction methods of the String class


Table 5-3 Search and extraction methods of the String class (cont’d.)


Replacing Characters and Substrings

• Replace() method: replaces all instances of a specified character or text within a string– Syntax: string.Replace(oldText, newText)

• Replace() method is case sensitive


Converting between Strings and Arrays

• Split() method: splits a string into an indexed array

• Syntax: array=string.Split(separator, [limit]);– separator argument: specifies the character

where the string will be separated into array element– limit argument: sets the maximum length of the

returned array


Converting between Strings and Arrays (cont’d.)

• Join() method: combines array elements into a string, separated by specified characters

• Syntax: stringVariable=String.Join

([“separator”], arrayName]);– separator argument: the character(s) that will

separate the contents of each array element in the returned string

• Can use an empty string to prevent elements from being separated by any characters in the new string


Comparing Strings• Comparison operators can be used with strings as

well as numbers• String class also provides comparison methods• Equals() method: compares two strings to

determine if they contain the same value

• Syntax: string.Equals(string);• Compare() method: compares two strings

• Syntax: string.Compare(string1,string2)– Returns 0 if string1 and string2 are equivalent– Returns >0 if string2 sorts before string1– Returns -1 if string1 sorts before string2


Comparing Strings (cont’d.)


Table 5-4 Comparison methods of the String class

Combining Characters and Substrings

• To combine text strings, you can use:– Concatenation operator (+) – Compound assignment operator (+=)– Concat() method of the String class

• Concat() method: creates a new string by combining strings passed as arguments

• Syntax: string.Concat(string1, string2, …)

• Insert() method: inserts text at the specified index position within the string

• Syntax: string.Insert(index,text)


Working with Regular Expressions

• Regular expressions: patterns used for matching and manipulating strings according to specified rules– Often used for validating submitted form data

• Must add a using directive to import the System.Text.RegularExpressions namespace to use regular expressions


Defining Regular Expressions in C#

• Regex() constructor: part of the Regex class, which represents regular expressions in C#

• Syntax: regExpName = new Regex(“pattern”);

• Use the Match class to determine if a string matches a regular expression pattern– Success property returns true if the regular

expression was found in the string being tested


Writing Regular Expression Patterns

• Regular expression patterns contain literal characters and metacharacters

• Metacharacters: special characters that define pattern matching rules in regular expressions


Writing Regular Expression Patterns (cont’d)


Table 5-5 Regular expression metacharacters

Matching Any Character

• Period (.): – Match any single character – A character must appear in the location where the

period appears in the pattern

• Example: Regex zipPattern = new Regex(“…..”);


Matching Characters at the Beginning or End of a String

• Anchor: a pattern that matches the beginning or end of a line– Must use a metacharacter to specify the matching

• ^ metacharacter matches characters at the beginning of a string

• $ metacharacter matches characters at the end of a string

• All literals following the ^ or preceding the $ compose the anchor

• Example: Regex urlProtocol = new Regex(“^http”);


Matching Special Characters

• To match any metacharacters as literal values in a regex, precede the character with a backslash to “escape” the metacharacter– Must also precede the pattern string with @ to force

C# to ignore the escaped character

• Example: to ensure that a string contains a periodRegex urlIdentifier = new RegEx(@”\.com”);


Specifying Quantity

• Quantifier: a metacharacter that specifies the number of matches desired

• ? specifies that the preceding character in the pattern is optional

• + specifies that one or more of the preceding characters match

• * specifies that zero or more of the preceding characters match

• {n} specifies the precise number of times that a character must repeat


Specifying Quantity (cont’d.)


Table 5-6 Regular expression quantifiers

Specifying Subexpressions

• Subexpression (or subpattern): a portion of the pattern enclosed in parentheses– Allows you to specify the format and quantities of the

enclosed characters as a group

• Example: regex for a telephone number“^(1-)?($.{3}$ )?(.{3})(\-.{4})$”

– Optionally includes 1 and area code, followed by a space

– Includes two groups of numbers, one with 3 and one with 4, separated by a hyphen


Defining Character Classes

• Character classes: used in regular expressions to treat multiple characters as a single item– Created by enclosing the characters that make up

the class in square brackets [ ]– Any character in the class represents an alternate

character that would be accepted as a match

• Example: Regex aWord = new Regez(“analy[sz]e”);

• Use a hyphen to specify a range of values– Example: [a-z] is all lowercase letters


Defining Character Classes (cont’d.)

• Use the ^ metacharacter before optional characters to be excluded– Example: exclude letters E and G through Z

Regex grade = new Regex(“[^EG-Z]”);

• Can combine ranges in a character class– Example: include all alphanumeric characters

Regex alpha = new Regex(“[0-9a-zA-Z]”);

• Can use special escape characters to represent common types of data:– \w for all alphanumeric characters



Table 5-7 Character class escape characters

Defining Character Classes (cont’d.)

Matching Multiple Pattern Choices

• Use the Or metacharacter (|) to specify an alternate set of substrings

• Example: check that a Web site domain ends in .com, .org, or .net

Regex url = new Regex

(@”\.(com|org|net)$”);


Setting Regular Expression Options

• RegexOptions enumeration: used to set how C# executes regular expressions

• Enumeration: a C# construct containing a set of named constants called an enumerator list

• IgnoreCase enumerator: determines whether to ignore the case of a letter– Passed as a second argument– Example: Regex url = new Regex

(@”\.(com|org|net)$”, RegexOptions.IgnoreCase);


Setting Regular Expression Options (cont’d.)

• Use the piping symbol (|) to separate multiple RegexOption enumerators

• IgnorePatternWhitespace enumerator: ignores any white space– Example:

Regex url = new Regex (@”\.(com|org|net)$”, RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace);


Using the RegularExpressionValidator Control

• RegularExpressionValidator control: used to programmatically validate a regular expression – ControlToValidate property: field to be validated– ValidationExpression property: the regular

expression pattern to be used


Summary

• Parsing: the act of extracting characters or substrings• String class is used to represent all literal strings

and string variables in C#

• Simple Mail Transport Protocol (SMTP): protocol used by most e-mail systems

• Namespace: an abstract container that manages identifiers in a C# program

• MailMessage class: used to create an e-mail object• MailAddress class: used to identify e-mail address

and display name of the sender


Summary (cont’d.)• Use ASP.NET Web Site Administration Tool to

administer and configure a Web site• SmtpClient class: allows you to send e-mail

messages with SMTP• Length property of the String class returns the

number of characters in a string• IsNullOrEmpty() method determines if a string

variable contains characters or is empty• String class methods allow changing character

case, trimming spaces, removing characters from start or end of a string, and search and extraction of substrings


Summary (cont’d.)

• String class’s Chars property retrieves a character by its index position

• Replace() method replaces text within a string• Split() method splits a string into an indexed

array• Join() method combines array elements into a

string, separated by specified characters• Concat() method creates a new string by

combining strings• Insert() method inserts text at the specified

index position in a stringASP.NET Programming with C# and SQL Server, First Edition 46

Summary (cont’d.)

• Regular expressions are patterns used for matching strings

• Regex constructor is used to define a regular expression

• Regex class contains methods and properties for working with regular expressions

• Match class used to determine if a string matches a regular expression pattern

• Regular expression patterns contain literal characters and metacharacters


Summary (cont’d.)

• Use a period to match any single character

• An anchor is a pattern that matches the start or end of a line, specified with the ^ metacharacter

• To match a metacharacter as a literal value, precede it with a backslash

• Quantifiers specify the number of matches desired

• Characters in parentheses are called subexpressions

• Use character classes to treat multiple characters as a single item


Summary (cont’d.)

• Separate alternate sets of substrings with the | metacharacter

• Use RegexOptions enumeration to configure how C# executes regular expressions

• Enumeration is a C# construct that contains a set of named constants

• RegularExpressionValidator control is used to programmatically validate a regular expression


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ASP.NET Programming with C# and SQL Server First Edition Chapter 5 Manipulating Strings with C#