C# expression
last modified July 5, 2023
In this article we work with expressions in C#.
An expression is a unit of code that evaluates to a value.
Expressions are constructed from operands and operators. The operators of an expression indicate which operations to apply to the operands.
There are several types of expressions in C#:
- lambda expressions
- query expressions
- switch expressions
- with expressions
- interpolated string expressions
- expression body definitions
Func<int, int> square = (int x) => x * x;
On the right side of the assignment, we have a function body expression. The expression results in a value.
Console.WriteLine("falcon");
In contrast, a statement such as writing to a console, does not result in a value.
C# lambda expression
A lambda expression is an anonymous function not bound to an
identifier. The lambda declaration operator => to separate the
lambda's parameter list from its 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));
In the example, we filter out all positive values from an array of integers.
The Array.FindAll function takes a predicate function as a second
parameter. With (e) => e > 0 lambda expression we define this
predicate.
$ dotnet run 1 3 4 2 1 3
C# query expression
A query expression allows us to extract and transform data in C# with 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));
In the example, we use a query expression to find all even values in an array.
$ dotnet run -2 4 6 2 0 -4 2 8
C# switch expression
The switch expression provides branching control that is based on the comparison of an expression with a set of patterns. Unlike classic switch keyword, it returns the value of the matching arm.
int age = 23;
string name = "Peter";
List<string> colors = new List<string> {"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<string> => "list of strings",
Array => "array",
_ => "unknown"
};
In the example, we find out the data type of a variable using switch expression.
$ dotnet run integer string list of strings array
C# with expression
The with expression produces a copy of its operand with the specified properties and fields modified.
Point p1 = new Point(0, 0);
Point p2 = p1 with { y = 3 };
Console.WriteLine(p1);
Console.WriteLine(p2);
record Point(int x, int y);
In the example, we create a copy of a point with its y member
modified to 3.
$ dotnet run
Point { x = 0, y = 0 }
Point { x = 0, y = 3 }
C# interpolated string expressions
We can put expressions inside interpolated strings to create formatted strings.
Interpolated strings are prefixed with the $ character.
int x = 5;
int y = 6;
Console.WriteLine($"{x} * {y} = {x * y}");
In the example, we create a string in which we multiply two values.
$ dotnet run 5 * 6 = 30
C# expression body definitions
Expression body definitions provide a concise definition for a function, constructor, property, indexer, or finalizer.
Func<int, int> 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}";
}
In the program, we have an expression body definition for the
square function, User constructor, and
ToString member function.
$ dotnet run 25 John Doe is a gardener
Source
Expressions - language reference
In this article we have worked with expressions in C#.
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