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?: operator - the ternary conditional operator
Learn about the C# ternary conditional operator, (`?:`), that returns the result of one of the two expressions based on a Boolean expression's result.
11/29/2022
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?: operator [C#]
conditional operator (?:) [C#]

?: operator - the ternary conditional operator

The conditional operator ?:, also known as the ternary conditional operator, evaluates a Boolean expression and returns the result of one of the two expressions, depending on whether the Boolean expression evaluates to true or false, as the following example shows:

:::code language="csharp" interactive="try-dotnet-method" source="snippets/shared/ConditionalOperator.cs" id="BasicExample":::

As the preceding example shows, the syntax for the conditional operator is as follows:

condition ? consequent : alternative

The condition expression must evaluate to true or false. If condition evaluates to true, the consequent expression is evaluated, and its result becomes the result of the operation. If condition evaluates to false, the alternative expression is evaluated, and its result becomes the result of the operation. Only consequent or alternative is evaluated. Conditional expressions are target-typed. That is, if a target type of a conditional expression is known, the types of consequent and alternative must be implicitly convertible to the target type, as the following example shows:

:::code language="csharp" source="snippets/shared/ConditionalOperator.cs" id="TargetTyped":::

If a target type of a conditional expression is unknown (for example, when you use the var keyword) or the type of consequent and alternative must be the same or there must be an implicit conversion from one type to the other:

:::code language="csharp" source="snippets/shared/ConditionalOperator.cs" id="NotTargetTyped":::

The conditional operator is right-associative, that is, an expression of the form

a ? b : c ? d : e

is evaluated as

a ? b : (c ? d : e)

Tip

You can use the following mnemonic device to remember how the conditional operator is evaluated:

is this condition true ? yes : no

Conditional ref expression

A conditional ref expression conditionally returns a variable reference, as the following example shows:

:::code language="csharp" interactive="try-dotnet-method" source="snippets/shared/ConditionalOperator.cs" id="ConditionalRef":::

You can ref assign the result of a conditional ref expression, use it as a reference return or pass it as a ref, out, in, or ref readonly method parameter. You can also assign to the result of a conditional ref expression, as the preceding example shows.

The syntax for a conditional ref expression is as follows:

condition ? ref consequent : ref alternative

Like the conditional operator, a conditional ref expression evaluates only one of the two expressions: either consequent or alternative.

In a conditional ref expression, the type of consequent and alternative must be the same. Conditional ref expressions aren't target-typed.

Conditional operator and an if statement

Use of the conditional operator instead of an if statement might result in more concise code in cases when you need conditionally to compute a value. The following example demonstrates two ways to classify an integer as negative or nonnegative:

:::code language="csharp" source="snippets/shared/ConditionalOperator.cs" id="CompareWithIf":::

Operator overloadability

A user-defined type can't overload the conditional operator.

C# language specification

For more information, see the Conditional operator section of the C# language specification.

Specifications for newer features are:

See also