C# Strings – Complete Guide to Text Handling in C#

Introduction – Why Learn Strings in C#?

Strings are a cornerstone of application development. Whether you’re building a web form, processing file paths, or constructing JSON responses—strings play a pivotal role. In C#, strings are powerful, object-oriented, and immutable, offering numerous methods for manipulation, validation, and formatting.

In this guide, you’ll learn:

• What strings are and how they work in C#
• String declaration, formatting, and interpolation
• Common string methods and operations
• Immutable behavior and StringBuilder use
• Real-world examples and best practices

Core Concept – What Is a String in C#?

A string in C# is a sequence of Unicode characters represented by the System.String class. Strings are immutable, meaning any change results in a new string object.

Syntax:

string welcome = "Hello, World!";

Code Example – Basic String Operations

string firstName = "Alice";
string greeting = "Hello, " + firstName + "!";
Console.WriteLine(greeting);

Output:

Hello, Alice!

Explanation:

• Strings are concatenated using +.
• Immutable nature means a new string is returned after modification.

String Methods – Useful and Common Operations

string title = "  Learn C# Strings  ";

Console.WriteLine(title.Trim());             // Removes extra spaces
Console.WriteLine(title.ToUpper());          // Converts to uppercase
Console.WriteLine(title.Contains("C#"));     // Checks for substring
Console.WriteLine(title.Replace("C#", "CSharp")); // Replaces substring

Other Common Methods:

• .Length
• .ToLower()
• .Substring(start, length)
• .Split(delimiter)
• .StartsWith(), .EndsWith()
• .IndexOf()

String Interpolation – Clean, Readable Formatting

string name = "Bob";
int age = 30;

Console.WriteLine($"Name: {name}, Age: {age}");

Use Case: Simplifies formatting over + concatenation.

String Immutability & StringBuilder

Since strings are immutable, repeated modifications inside loops can lead to memory overhead. Use StringBuilder to optimize:

StringBuilder sb = new StringBuilder();
sb.Append("Welcome ");
sb.Append("to ");
sb.Append("C#");
Console.WriteLine(sb.ToString());

Use Case: Efficient when concatenating strings dynamically.

Escape Sequences

Verbatim Strings – Ignore Escapes Using @

string path = @"C:\Program Files\App";

Use Case: Clean file paths and multi-line strings.

String Comparison – Equals and Compare

string a = "Test";
string b = "test";

Console.WriteLine(a.Equals(b, StringComparison.OrdinalIgnoreCase)); // true

Use StringComparison.OrdinalIgnoreCase for case-insensitive checks.

Real-World Use Cases

• 📩 Formatting email templates
• Building URLs and API queries
• Validating passwords or inputs
• Generating reports, file content
• Processing CSV, JSON, or XML data

Summary – Recap & Next Steps

Key Takeaways:

• Strings are immutable and offer a rich API.
• Use interpolation for cleaner code, and StringBuilder for large dynamic operations.
• Methods like .Trim(), .Replace(), .Split() make manipulation easy.

Real-world relevance: Strings are central to data exchange, UI rendering, logging, and file handling in any .NET app.

FAQ Section

Are strings mutable in C#?
No, strings are immutable. Use StringBuilder for performance when changing values repeatedly.

What’s the difference between == and .Equals()?
Both compare values. .Equals() can be used with StringComparison for case sensitivity control.

How do I check for an empty or null string?
Use string.IsNullOrEmpty() or string.IsNullOrWhiteSpace().

Can I format numbers and dates in strings?
Yes. Use interpolated strings or string.Format():

string price = $"{123.45:C}";

How do I split a sentence into words?
Use .Split():

string[] words = sentence.Split(' ');