Reference - What does this symbol mean in C#?

Question

What is this?

This is a collection of questions that come up every now and then about syntax in C#. This is also a Community Wiki (or has been flagged for such), so everyone is invited to participate in maintaining this list.

Why is this?

Stack Overflow does not allow searching for particular characters. As a consequence, many questions about operators and other syntax tokens are not found easily when searching for them. This also makes closing duplicates more difficult. The list below is to help with this issue.

The main idea is to have links to existing questions on Stack Overflow, so it's easier for us to reference them, not to copy over content from the C# Spec.

Additionally, this is a blatant copy of the JS reference (and the PHP reference, the CSS reference, etc.). We needed a C# one.

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Please help. Edit and add links to other operators/syntax references, or if you can't find good questions/answers on a particular piece of syntax, add an answer to this question and link it

Answer 1

Please do note that a lot of questions about syntax can be answered by reading and searching the C# Language Specification and the more approachable C# Language Reference.

Headings for most syntax will be pulled from that reference, including C# Operators and expressions:

Operators

Arithmetic operators

% Remainder operator

• What does the '%' operator mean?

++ Postfix and prefix increment operator

• What is the difference between i++ and ++i?

Boolean logical operators

|| and | Conditional and Logical OR operators

• C# 'or' operator?
• What is the difference between the | and || or operators?

&& and & And operators

• C# & operator clarification

Bitwise and shift operators

~ Unary bitwise complement operator

• Bitwise "~" Operator in C#

<< Binary left shift operator

• What does the operator "<<" mean in C#?

^ Binary XOR (logical exclusive OR) operator

• When to use "^" operator

Equality operators

== Equality operator

• When is Double's == operator invoked?
• Operator '==' can't be applied to type T?
• How to define the operator ==

Member access operators and expressions

?. Null conditional operator

• What does the question mark in member access mean in C#?
• What does question mark and dot operator ?. mean in C# 6.0?

Type-testing operators and cast expression

is operator/pattern

• Why does is operator behave like == operator?

Assignment operators

op= Compound assignment operators

• C# '+=' Operator
• What does /= mean in C#?

+= and -= with events/delegates

• += operator with Events

?? Null coalescing operator

• What do two question marks together mean in C#?
• What is the operator precedence of C# null-coalescing (??) operator?

Lambda expressions

=> Lambda declaration operator

• What does the '=>' syntax in C# mean?

=> Expression-bodied members

• What does the => operator mean in a property?

Other operators

?: Conditional (Ternary) operator

• Question mark and colon in statement. What does it mean?
• Benefits of using the conditional ?: (ternary) operator

! Null-forgiving operator

• What does null! statement mean?

:: Namespace alias qualifier

• C# method call with parameter name and colon

true and false operators

• What's the false operator in C# good for?

new operator and keyword

• I don't understand why we need the 'new' keyword
• What does "A new expression requires (), [], or {} after type" mean?
• What does the new[] {string} syntax mean?
• What does int test[] = new int[0] mean?
• What does the keyword "new" do to a struct in C#?
• What does method ( new { x=y.property } ) mean?
• new keyword in method signature
• What does new() mean?

Other syntax

typeName? variableName Nullable value types

• What is the purpose of a question mark after a type (for example: int? myVariable)?

?[]? Nullable array of nullable reference types

• What is the ?[]? syntax in C#?

@ before variable names and before string literals

• when to use @ in c#?

$ before string literals

• What does $ mean before a string?

{0} (or any number) in strings

• What does {0} mean when found in a string in C#?

array[^1] Range and index types

• What does `array[^1]` mean in C# compiler?
• What are Range and Index types in C# 8?