question mark inside C# syntax [duplicate]

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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 ?

开发者_StackOverflow

Thanks in advance

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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.

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this is the same as

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

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It is the conditional operator.

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?: 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;

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

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

result = condition ? result_if_condition_true : result_if_condition_false

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