question mark inside C# syntax [duplicate]

Question

Possible Duplicate:
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

Answer 1

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.

Answer 2

this is the same as

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