C# Strings - Complete Guide
Introduction to Strings in C#
Strings in C# are sequences of characters represented by the System.String class. Strings are immutable: once created, they cannot be modified, and any change results in a new string object.
C# provides rich string manipulation features such as concatenation, searching, formatting, splitting, and more. Mastering string handling is essential for most applications.
String Declaration and Initialization
Strings can be declared in multiple ways using the string keyword, the String class, var, or verbatim literals.
Example
using System;
namespace StringDeclarationExample
{
class Program
{
static void Main(string[] args)
{
string str1 = "Hello, World!";
String str2 = "Hello, C#!";
var str3 = "Hello, Var!";
string empty1 = "";
string empty2 = string.Empty;
string nullString = null;
string multiLine = @"This is a
multi-line
string example";
Console.WriteLine(str1);
Console.WriteLine(str2);
Console.WriteLine(str3);
Console.WriteLine($"Empty1: '{empty1}', Empty2: '{empty2}'");
Console.WriteLine($"Null string: '{nullString}'");
Console.WriteLine($"Multi-line:\n{multiLine}");
Console.WriteLine($"Length of str1: {str1.Length}");
Console.WriteLine($"Is str1 null or empty? {string.IsNullOrEmpty(str1)}");
Console.WriteLine($"Is empty1 null or empty? {string.IsNullOrEmpty(empty1)}");
Console.WriteLine($"Is nullString null or empty? {string.IsNullOrEmpty(nullString)}");
}
}
}Output
Hello, World! Hello, C#! Hello, Var! Empty1: '' , Empty2: '' Null string: '' Multi-line: This is a multi-line string example Length of str1: 13 Is str1 null or empty? False Is empty1 null or empty? True Is nullString null or empty? True
String Immutability
Strings are immutable in C#. Operations that look like they change a string actually create new instances.
Use StringBuilder when working with many string modifications to improve performance.
Example
using System;
using System.Text;
namespace StringImmutabilityExample
{
class Program
{
static void Main(string[] args)
{
string original = "Hello";
string modified = original;
Console.WriteLine($"Original: {original}");
Console.WriteLine($"Modified: {modified}");
Console.WriteLine($"ReferenceEquals? {object.ReferenceEquals(original, modified)}");
modified += ", World!";
Console.WriteLine($"After modification -> Original: {original}, Modified: {modified}");
Console.WriteLine($"ReferenceEquals? {object.ReferenceEquals(original, modified)}");
string str1 = "Hello";
string str2 = "Hello";
string str3 = new string("Hello".ToCharArray());
Console.WriteLine($"str1 == str2: {str1 == str2}");
Console.WriteLine($"str1 == str3: {str1 == str3}");
Console.WriteLine($"ReferenceEquals(str1, str2): {object.ReferenceEquals(str1, str2)}");
Console.WriteLine($"ReferenceEquals(str1, str3): {object.ReferenceEquals(str1, str3)}");
StringBuilder sb = new StringBuilder();
sb.Append("Hello");
sb.Append(", World!");
Console.WriteLine($"StringBuilder result: {sb.ToString()}");
}
}
}Output
Original: Hello Modified: Hello ReferenceEquals? True After modification -> Original: Hello, Modified: Hello, World! ReferenceEquals? False str1 == str2: True str1 == str3: True ReferenceEquals(str1, str2): True ReferenceEquals(str1, str3): False StringBuilder result: Hello, World!
Common String Methods
The String class provides many built-in methods for trimming, searching, modifying, and formatting strings.
Example
using System;
namespace StringMethodsExample
{
class Program
{
static void Main(string[] args)
{
string text = " Hello, World! ";
Console.WriteLine($"Trimmed: '{text.Trim()}'");
Console.WriteLine($"ToUpper: {text.ToUpper()}");
Console.WriteLine($"ToLower: {text.ToLower()}");
string sentence = "The quick brown fox jumps over the lazy dog";
Console.WriteLine($"Contains 'fox'? {sentence.Contains("fox")}");
Console.WriteLine($"StartsWith 'The'? {sentence.StartsWith("The")}");
Console.WriteLine($"EndsWith 'dog'? {sentence.EndsWith("dog")}");
Console.WriteLine($"IndexOf 'brown': {sentence.IndexOf("brown")}");
Console.WriteLine($"Substring(10): {sentence.Substring(10)}");
Console.WriteLine($"Replace 'fox' with 'cat': {sentence.Replace("fox", "cat")}");
string[] words = sentence.Split(' ');
Console.WriteLine("Split into words:");
foreach (var w in words)
{
Console.WriteLine(w);
}
string joined = string.Join("-", words);
Console.WriteLine($"Joined: {joined}");
string formatted = string.Format("Hello, {0}! Today is {1:yyyy-MM-dd}", "Alice", DateTime.Now);
Console.WriteLine(formatted);
}
}
}Output
Trimmed: 'Hello, World!' ToUpper: HELLO, WORLD! ToLower: hello, world! Contains 'fox'? True StartsWith 'The'? True EndsWith 'dog'? True IndexOf 'brown': 10 Substring(10): brown fox jumps over the lazy dog Replace 'fox' with 'cat': The quick brown cat jumps over the lazy dog Split into words: The quick brown fox jumps over the lazy dog Joined: The-quick-brown-fox-jumps-over-the-lazy-dog Hello, Alice! Today is 2023-10-15