question mark inside C# syntax

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Benefits of using the conditional ?: (ternary) operator

hi, I'm viewing this freesource library and I saw this weird - at least for me - syntax

*currFrame = ( ( diff >= differenceThreshold ) || ( diff <= differenceThresholdNeg ) ) ? (byte) 255 : (byte) 0;

currFrame is of type byte

diff, differenceThreshold and differenceThresholdNeg are of type Int.

What does the question mark do ? , what is this weird assign sentence suppose to mean ?

Thanks in advance

right, [link](http://stackoverflow.com/questions/5136293/what-is-this-weird-syntax-in-c-byte) — musaab, Feb 28 '11 at 17:57

Jakub Konecki · Accepted Answer · 2011-02-28T15:03:07.860

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;

C# reference: http://msdn.microsoft.com/en-us/library/ty67wk28.aspx

In your case currFrame will be assigned a value of 255 if ( diff >= differenceThreshold ) || ( diff <= differenceThresholdNeg ) is true, otherwise value 0 will be assigned.

score 7 · Answer 2 · answered Feb 28 '11 at 14:40

7

this is the same as

if(( diff >= differenceThreshold ) || ( diff <= differenceThresholdNeg ) )
     currFrame = (byte) 255
else
    currFrame = (byte) 0

answered Feb 28 '11 at 14:40

JAiro

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Yuriy Faktorovich · Answer 3 · 2011-02-28T14:44:45.387

4

It is the conditional operator.

edited Feb 28 '11 at 14:44

answered Feb 28 '11 at 14:39

Yuriy Faktorovich

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2

Its *name* is the conditional operator though. It happens to be the only ternary operator currently in C#, but it's worth calling it by its name rather than just identifying it by the number of operands, IMO. – Jon Skeet Feb 28 '11 at 14:43
2

It is *a* ternary operator. It's specifically the conditional operator. Whilst, at present, C# exposes only a single ternary operator, you wouldn't go around referring to `+` as "the binary operator" – Damien_The_Unbeliever Feb 28 '11 at 14:43
I'll bow to peer pressure and put conditional. – Yuriy Faktorovich Feb 28 '11 at 14:45

score 3 · Answer 4 · answered Feb 28 '11 at 14:40

3

?: Operator (C# Reference):

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

condition ? first_expression : second_expression;

answered Feb 28 '11 at 14:40

CD..

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score 1 · Answer 5 · answered Feb 28 '11 at 14:39

1

'?:' is a conditional operator, you can read about it here: http://msdn.microsoft.com/en-us/library/ty67wk28(v=vs.80).aspx

answered Feb 28 '11 at 14:39

tpeczek

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score 0 · Answer 6 · answered Feb 28 '11 at 14:40

0

This is a ternary operator (see MSDN). It follows the following syntax:

result = condition ? result_if_condition_true : result_if_condition_false

answered Feb 28 '11 at 14:40

Matthew Abbott

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It's a ternary operator *called* the conditional operator. – Jon Skeet Feb 28 '11 at 14:45

score 0 · Answer 7 · answered Feb 28 '11 at 14:41

0

if ( diff >= differenceThreshold ) || ( diff <= differenceThresholdNeg ) ) 
*currFrame = (byte) 255;
else *currFrame =  (byte) 0;

answered Feb 28 '11 at 14:41

Erix

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question mark inside C# syntax

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