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?: Operator (C# Reference)

Visual Studio 2008

The conditional operator (?:) returns one of two values depending on the value of a Boolean expression. Following is the syntax for the conditional operator.

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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 check for a possible division-by-zero error before calculating the sin function.

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if(x != 0.0) s = Math.Sin(x)/x; else s = 1.0;
s = x != 0.0 ? Math.Sin(x)/x : 1.0;

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.

C#
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class ConditionalOp
{
    static double sinc(double x)
    {
        return x != 0.0 ? Math.Sin(x) / x : 1.0;
    }

    static void Main()
    {
        Console.WriteLine(sinc(0.2));
        Console.WriteLine(sinc(0.1));
        Console.WriteLine(sinc(0.0));
    }
}
/*
Output:
0.993346653975306
0.998334166468282
1
*/
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Something to watch out for
float yourFloat = 10.0f;
int yourInt = 5;
object someValue = condition ? yourInt : yourFloat;

This might not get you exactly what you expected; you would probably expect to get an int if 'condition' is true, and a float if 'condition' is false, but, the compiler will actually cast yourInt to a float -- resulting in someValue always being a float.

This particularly annoyed me, because I was using ToString() on it, which obviously wouldn't work out if I expected an int, but got a float instead (since the string representation is completely different).
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?: vs if() condition
Hi Guys,

I am just confused on which should be used when.
When should we use ?: and when should we use if() and which is better one.

Thanks,
Ajay Matharu
http://www.ajaymatharu.com
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