Strings & String Interpolation

Syntax

string variableName = $"text {expression}";

Examples

string firstName = "Fola";
string lastName = "A";

string fullName = firstName + " " + lastName;
Console.WriteLine(fullName);  // Fola A

string greeting = string.Format("Hello, {0}!", firstName);
Console.WriteLine(greeting);

string name = "Fola";
int age = 21;
double price = 19.5;

Console.WriteLine($"{name} is {age} years old");
Console.WriteLine($"Price: ${price:F2}");        // Price: $19.50
Console.WriteLine($"{name.ToUpper()} says hi");   // expressions work too

string path = @"C:\Users\Fola\Documents";  // no need to double-escape backslashes
Console.WriteLine(path);

string multiLine = @"Line one
Line two
Line three";
Console.WriteLine(multiLine);

// Raw string literals (C# 11+) go even further
string json = """{"name": "Fola"}""";
Console.WriteLine(json);

string text = "  Hello World  ";

Console.WriteLine(text.Length);          // 17 (includes whitespace)
Console.WriteLine(text.Trim());           // "Hello World"
Console.WriteLine(text.ToUpper());        // "  HELLO WORLD  "
Console.WriteLine(text.Trim().Substring(0, 5));  // "Hello"
Console.WriteLine(text.Contains("World")); // true

Best practices

• Use string interpolation ($"...") instead of string.Format() or + concatenation - it is more readable and just as efficient
• Use a StringBuilder instead of repeated + concatenation when building a large string inside a loop, for much better performance
• Use verbatim strings (@"...") for file paths and regular expressions to avoid a wall of doubled backslashes
• Remember string is immutable - every "modifying" method like .Trim() or .ToUpper() returns a new string rather than changing the original

At a glance

Purpose

Applications on the .NET platform

File extension

.cs

Runs in

.NET runtime

Usually used with

.NET SDK and libraries

Specifications & further reading

• C# language reference

Related C# documentation