The document discusses immutable and mutable strings in .NET. Immutable strings created with the String class cannot be modified - methods return new strings rather than modifying the original. Mutable strings created with StringBuilder can be modified in-place with methods like Append() and Insert(). Regular expressions provide a tool for text searching and manipulation using literals to match text and metacharacters to provide commands.

1. Chapter 10
Immutable Strings
string objects are immutable, i.e. we cannot modify the characters contained in them. The string is an
alias for the predefined System.String class in the Common Language Runtime (CLR). The build-in
operations produce a modified version of the string rather than modifying the string on which the
method is called.
Compare() – Compares the strings CompareTo() – Compares the current instance
with another instance
ConCat() – Concatenates two or more strings Copy() – Creates a new string by copying another
CopyTo() – Copies a specified number of chars to
an array of Unicode chars
Equals() – Determines if two strings are equal
Join() – Joins an array of strings together PadLeft() – Left-aligns the strings in a field
PadRight() – Right-aligns the strings in a field Remove () – Deletes characters from the string
Substring() – Extracts a suvbstring ToLower() – Returns a lower-case version of
string
ToUpper() - Returns a upper-case version of string Trim() – Removes white space from the string
TrimEnd() – Removes a string of characters from
the end of the string
TrimStart() – Removes a string of characters from
beginning of the string
Mutable Strings
Mutalbe strings that are modifiable can be created using StringBuilder class
Eg. StringBuilder str1 = new StringBuilder(“abc”);
They grow dynamically as more characters are added to them. Mutable strings are also known as
dynamic strings.
StringBuilder Methods are :
- Append() – Appends a string,
AppendFormat() – Appends strings using a specific format
EnsureCapacity()
– Ensures sufficient size,
Insert() – Inserts a string at a specified position,
Remove() Removes the specified characters
Replace () – Replaces all instances of a character with the specified one

2. StringBuilder Properties :- Capacity – To retrieve or set the number of characters the object can hold,
Length – To retrieve or set the length
MaxCapacity – To retrieve the maximum capacity of the object,
[ ] – To get or set a character at a specified position
Regular Expressions
- Regular expressions provide a powerful tool for searching and manipulating a large text.
- A regular expression may be applied to a text to accomplish tasks such as
a) to locate the substrings and locate them
b) to modify one or more substrings and return
c) to identify substrings that begin with or end with a pattern of characters
d) to find all words that begin with a group of characters and end with some other characters.
e) To find all the occurrences of a substring patterns
- A regular expression also known as a pattern string is a string containing two types of characters
Literals, Metacharacters, Literals are characters that search and match in the text. Metacharacters are
special characters that give commands to the regular expression parser.
Eg of regular Expressions are “bm” – Any word beginning with m, “erb” – Any word ending
with er “BxB” – Any x in middle of word.
“bms*erb” – Any word beginning with m and ending with er “|,” – Any word separated by a
space or comma
Here, b, B, s* are metacharacters and m, er, x, comma are literals.
The namespace System.Text.RegularExpressions support a number of classes that can be used for
searching, matching and modifying a text document. The important classes are Regex, MatchCollection,
Match
Distinguish between String and StringBuilder class
String Class – The string class lies in the
namespace System
StringBuilder Class – the StringBuilder class lies in
the namespace System.Text
Immutable strings i.e. a string whose character
cannot be modified can be created using the
string class
Mutable strings can be created using the StringBuilder
class.
All operations produce a modified version of
string rather than modifying the string on
which the method is called.
All operation modify the original string on which the
method is called. Hence these type of strings are also
known as dynamic strings.