?: Operator (C# Reference)
The conditional operator (?:) returns one of two values depending on the value of a Boolean expression. Following is the syntax for the conditional operator.
condition ? first_expression : second_expression;
The condition must evaluate to true or false. If condition is true, first_expression is evaluated and becomes the result. If condition is false, second_expression is evaluated and becomes the result. Only one of the two expressions is evaluated.
Either the type of first_expression and second_expression must be the same, or an implicit conversion must exist from one type to the other.
You can express calculations that might otherwise require an if-else construction more concisely by using the conditional operator. For example, the following code uses first an if statement and then a conditional operator to classify an integer as positive or negative.
int input = Convert.ToInt32(Console.ReadLine()); string classify; // if-else construction. if (input < 0) classify = "negative"; else classify = "positive"; // ?: conditional operator. classify = (input < 0) ? "negative" : "positive";
The conditional operator is right-associative. The expression a ? b : c ? d : e is evaluated as a ? b : (c ? d : e), not as (a ? b : c) ? d : e.
The conditional operator cannot be overloaded.