Working with Strings

Strings are one of the most commonly used data types in programming. In this lesson, you'll learn how to create and manipulate strings in C#.

What is a String?

A string is a sequence of characters enclosed in double quotes.

csharp
1string greeting = "Hello, World!";
2string name = "Alice";
3string empty = "";

String Concatenation

Combine strings using the + operator:

csharp
1string firstName = "John";
2string lastName = "Doe";
3
4// Concatenation with +
5string fullName = firstName + " " + lastName;
6Console.WriteLine(fullName);  // John Doe
7
8// Building a message
9string message = "Hello, " + firstName + "!";
10Console.WriteLine(message);  // Hello, John!

String Interpolation

A cleaner way to embed values in strings using $:

csharp
1string name = "Alice";
2int age = 30;
3double height = 1.75;
4
5// String interpolation
6Console.WriteLine($"Name: {name}");
7Console.WriteLine($"Age: {age}");
8Console.WriteLine($"{name} is {age} years old");
9
10// Expressions inside braces
11Console.WriteLine($"Next year, {name} will be {age + 1}");
12Console.WriteLine($"Height in cm: {height * 100}");

Formatting with Interpolation

csharp
1double price = 19.99;
2DateTime today = DateTime.Now;
3
4// Format numbers
5Console.WriteLine($"Price: {price:C}");      // Price: $19.99 (currency)
6Console.WriteLine($"Price: {price:F1}");     // Price: 20.0 (1 decimal)
7
8// Format dates
9Console.WriteLine($"Date: {today:d}");       // Short date
10Console.WriteLine($"Date: {today:yyyy-MM-dd}"); // 2024-01-15
11
12// Alignment
13Console.WriteLine($"|{name,10}|");   // Right-align in 10 chars
14Console.WriteLine($"|{name,-10}|");  // Left-align in 10 chars

Escape Sequences

Special characters in strings:

csharp
1// Common escape sequences
2Console.WriteLine("Hello\tWorld");     // Tab
3Console.WriteLine("Line 1\nLine 2");   // New line
4Console.WriteLine("She said \"Hi\"");  // Quotes
5Console.WriteLine("Path: C:\\Users");  // Backslash
6
7// All escape sequences
8// \t  Tab
9// \n  New line
10// \\  Backslash
11// \"  Double quote
12// \'  Single quote
13// \r  Carriage return

Verbatim Strings

Use @ for strings that should be taken literally (no escape processing):

csharp
1// Without verbatim (need to escape backslashes)
2string path1 = "C:\\Users\\Documents\\file.txt";
3
4// With verbatim (no escaping needed)
5string path2 = @"C:\Users\Documents\file.txt";
6
7// Multi-line verbatim strings
8string multiLine = @"This is line 1
9This is line 2
10This is line 3";
11
12// To include quotes in verbatim strings, double them
13string quoted = @"He said ""Hello""";

Raw String Literals (C# 11+)

For complex strings with quotes and special characters:

csharp
1// Raw string literal (three or more quotes)
2string json = """
3    {
4        "name": "Alice",
5        "age": 30
6    }
7    """;
8
9// Interpolated raw strings
10string name = "Alice";
11string data = $"""
12    Name: {name}
13    Status: Active
14    """;

Common String Properties and Methods

csharp
1string text = "Hello, World!";
2
3// Properties
4int length = text.Length;           // 13
5
6// Case conversion
7string upper = text.ToUpper();      // HELLO, WORLD!
8string lower = text.ToLower();      // hello, world!
9
10// Searching
11bool contains = text.Contains("World");  // true
12int index = text.IndexOf("World");       // 7
13bool starts = text.StartsWith("Hello");  // true
14bool ends = text.EndsWith("!");          // true
15
16// Extracting
17string sub = text.Substring(0, 5);   // Hello
18char first = text[0];                // H
19
20// Modifying (returns new string)
21string replaced = text.Replace("World", "C#");  // Hello, C#!
22string trimmed = "  hello  ".Trim();            // hello

String Comparison

csharp
1string a = "hello";
2string b = "Hello";
3
4// Case-sensitive comparison
5bool equal1 = a == b;                    // false
6bool equal2 = a.Equals(b);               // false
7
8// Case-insensitive comparison
9bool equal3 = a.Equals(b, StringComparison.OrdinalIgnoreCase);  // true
10bool equal4 = string.Equals(a, b, StringComparison.OrdinalIgnoreCase);  // true

Null and Empty Strings

csharp
1string empty = "";
2string nullString = null;
3string whitespace = "   ";
4
5// Checking for empty or null
6bool isEmpty = string.IsNullOrEmpty(empty);           // true
7bool isNullOrEmpty = string.IsNullOrEmpty(nullString); // true
8bool hasContent = string.IsNullOrWhiteSpace(whitespace); // true
9
10// Safe way to work with potentially null strings
11string name = null;
12int length = name?.Length ?? 0;  // 0 (null-conditional + null-coalescing)

Building Strings Efficiently

For many concatenations, use StringBuilder:

csharp
1using System.Text;
2
3// Inefficient for many concatenations
4string result = "";
5for (int i = 0; i < 1000; i++)
6{
7    result += i + ", ";  // Creates new string each time
8}
9
10// Efficient alternative
11StringBuilder sb = new StringBuilder();
12for (int i = 0; i < 1000; i++)
13{
14    sb.Append(i);
15    sb.Append(", ");
16}
17string result = sb.ToString();

Summary

In this lesson, you learned:

• Strings are sequences of characters in double quotes
• Concatenate with + or use interpolation with $"...{value}..."
• Use escape sequences (\n, \t, \\) for special characters
• Use verbatim strings (@"...") for paths and multi-line text
• Common methods: Length, ToUpper(), Contains(), Substring(), Replace()
• Check for null/empty with string.IsNullOrEmpty()

Next, we'll learn how to convert between different data types.