C# expression

last modified April 22, 2025

This article explores the use of expressions in C# programming.

An expression is a code unit that evaluates to a single value.

Expressions consist of operands and operators, where operators specify the operations to be performed on the operands.

C# supports various types of expressions, including:

• lambda expressions
• query expressions
• switch expressions
• with expressions
• interpolated string expressions
• expression body definitions

Func square = (int x) => x * x;

The right side of this assignment features a function body expression, which yields a computed value.

Console.WriteLine("falcon");

Conversely, a statement, like console output, does not produce a value.

C# lambda expression

A lambda expression is an anonymous function without a fixed identifier, using the => operator to separate parameters from the body.

int[] vals = { 1, -2, 3, 4, 0, -3, 2, 1, 3 };
var res = Array.FindAll(vals, (e) => e> 0);
Console.WriteLine(string.Join(" ", res));

This example filters positive integers from an array using a lambda expression (e) => e> 0 as a predicate for Array.FindAll.

$ dotnet run
1 3 4 2 1 3

C# query expression

A query expression enables data extraction and transformation in C# through structured queries.

int[] vals = { -2, 4, 6, -1, 2, 0, 1, -3, -4, 2, 3, 8 };
var evens = 
 from val in vals
 where val % 2 == 0
 select val;
Console.WriteLine(string.Join(" ", evens));

This example employs a query expression to identify all even numbers in an array of integers.

$ dotnet run
-2 4 6 2 0 -4 2 8

C# switch expression

A switch expression facilitates branching by comparing an expression against patterns, returning the value of the matched arm, unlike traditional switch statements.

int age = 23;
string name = "Peter";
List colors = new List {"blue", "khaki", "orange"};
var nums = new int[] {1, 2, 3, 4, 5};
Console.WriteLine(check(age));
Console.WriteLine(check(name));
Console.WriteLine(check(colors));
Console.WriteLine(check(nums));
object check(object val) => val switch 
{
 int => "integer",
 string => "string",
 List => "list of strings",
 Array => "array",
 _ => "unknown"
};

This example uses a switch expression to determine the data type of various variables.

$ dotnet run
integer
string
list of strings
array

C# with expression

A with expression creates a modified copy of an operand, altering specified properties or fields.

Point p1 = new Point(0, 0);
Point p2 = p1 with { y = 3 };
Console.WriteLine(p1);
Console.WriteLine(p2);
record Point(int x, int y);

This example generates a copy of a point, modifying its y coordinate to 3 using a with expression.

$ dotnet run
Point { x = 0, y = 0 }
Point { x = 0, y = 3 }

C# interpolated string expressions

Interpolated string expressions, prefixed with $, allow embedding expressions within strings for dynamic formatting.

int x = 5;
int y = 6;
Console.WriteLine($"{x} * {y} = {x * y}");

This example constructs a formatted string by embedding a multiplication expression within an interpolated string.

$ dotnet run
5 * 6 = 30

C# expression body definitions

Expression body definitions offer a concise syntax for defining functions, constructors, properties, indexers, or finalizers.

Func square = (int x) => x * x;
int r = square(5);
Console.WriteLine(r);
var u = new User("John Doe", "gardener");
Console.WriteLine(u);
class User
{
 public User(string name, string occupation) =>
 (Name, Occupation) = (name, occupation);
 public string Name { get; set; }
 public string Occupation { get; set; }
 public override string ToString() => $"{Name} is a {Occupation}";
}

This program demonstrates expression body definitions for a square function, a User constructor, and a ToString method.

$ dotnet run
25
John Doe is a gardener

Source

Expressions - language reference

This article has demonstrated working with various expressions in C#.

Author

I am Jan Bodnar, a dedicated programmer with extensive experience in software development. Since 2007, I have authored over 1,400 programming articles and eight e-books. With more than a decade of teaching programming, I share my expertise through comprehensive tutorials.

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