Strings in C# can be manipulated using the System.String class. Strings can be immutable, using the standard string type, or mutable, using the StringBuilder class. Various methods like Compare(), Equals(), and == operator can be used to compare strings. Regular expressions allow searching, matching, and modifying strings using classes like Regex, MatchCollection, and Match.

1. Strings in C#
Dr. Neeraj Kumar Pandey

2. Strings in C#
 In C# System.String class is used to manipulate strings.
 System.String is a very powerful and versatile class, but it is not by
any means the only string-related class in the .NET armory.
 System.Text and System.Text.RegularExpression namespaces are
also used in Building Strings,Formatting Expressions and Regular
Expression
Dr. Neeraj Kumar
Pandey

3. Immutable Strings
 In this type of strings, we cannot modify the characters of a string.
Dr. Neeraj Kumar
Pandey

4. Immutable Strings
Dr. Neeraj Kumar
Pandey

5. Comparing Strings
Compare() Method
int n=string.Compare(s1,s2);
 Zero interger, if s1 is equal to s2
 A positive Integer (1) , if s1 is greater than s2
 A negative integer(-1), if s1 is less than s2
Equals() Method
There are two versions of Equals method. They are implemented as follows:-
bool b1= s2.Equals(s1);
bool b2= string.Equals(s2,s1);
These methods returns a Boolean value true if s1 and s2 are equal, otherwise false.
The == Operator
bool b3= (s1==s2); //b3 is true if they are equal
We very often use such statements in decision statements, like:-
if(s1==s2)
Dr. Neeraj Kumar
Pandey

6. Mutable Strings
 This type of strings are modifiable using the StringBuilder class.
StringBuilder str1=new StringBuilder(“hello”);
StringBuilder str2=new StringBuilder();
 They can grow dynamically as more characters are added to them.
 They can grow either unbounded or up to a configurable maximum.
 Mutable Strings are also known as dynamic strings.
Dr. Neeraj Kumar
Pandey

7. Mutable Strings(Contd..)
 The System.Text namespace contains the class StringBuilder,
therefore we must include the using System.Text directive for
creating and manipulating mutable strings.
Dr. Neeraj Kumar
Pandey

8. Mutable String Program
using System;
using System.Text;
class strbuild
{
public static void Main()
{
string str1,str2;
Console.WriteLine("Enter first string");
str1=Console.ReadLine();
Console.WriteLine("Enter Second string");
str2=Console.ReadLine();
StringBuilder s1 = new StringBuilder(str1);
StringBuilder s2 = new StringBuilder(str2);
//1.Appending a String
s1.Append("Smile");
// Console.WriteLine("String After Append :" +s1);
//2.Append Format
s2.AppendFormat("1)s2 after Append Format {0}",s2);
s1.AppendFormat("2)s1 after Append Format {0}",s1);
//3.Ensure Capacity
int x=s1.EnsureCapacity(30);
//4.Inserting a String
s2.Insert(3,"Life");
//5.Remove
s1.Remove(5,3);
//6.Replace
s2.Replace('A', '*');
//7.Capacity
int y= s1.Capacity;
Console.WriteLine("Capacity is"+y);
s1.Capacity=100;
y=s1.Capacity;
Console.WriteLine("New Capacity is"+y);
//8.Length
int z = s1.Length;
int v = s2.Length;
Console.WriteLine(" Length of s1 "+ z);
Console.WriteLine("Length of s2"+ v);
//9.MaxCapacity
int c= s1.MaxCapacity;
Console.WriteLine("Max Capacity"+s1);
//10.setting a character
int n=s2.Length;
s2[n-1]='@';
}
}
Dr. Neeraj Kumar
Pandey

9. Regular Expression
 A regular expression may be applied to a text to accomplish tasks
such as :-
 To locate substring and return them
 To modify one or more substrings and return them
 To identify substrings that begins with or end with a pattern of
characters.
 To find all the words that begin with a group of characters and end
with some other characters
 To find all the occurrences of a substring pattern.
 System.Text.RegualrExpressions supports a number of classes that
can be used for searching, matching and modifying a text
document.The important classes are:-
 Regex, MathCollection, Match.
Dr. Neeraj Kumar
Pandey

10. Regular Expression Program
using System;
using System.Text;
using System.Text.RegularExpressions;
class bulb
{
public static void Main()
{
string str;
str= Console.ReadLine();
Regex reg= new Regex(" |, ");
StringBuilder sb= new StringBuilder();
int count=1;
foreach(string sub in reg.Split(str))
{
sb.AppendFormat("{0}:{1}n",count++,sub);
}
Console.WriteLine(sb);
}
}
Dr. Neeraj Kumar
Pandey