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.
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?: Operator (C# Reference)