Boolean parameter with check up

This is called the 'ternary operator', you will find a clear and concise description at http://www.cprogramming.com/reference/operators/ternary-operator.html or http://www.cplusplus.com/articles/1AUq5Di1/ (as well as http://en.wikipedia.org/wiki/%3F: - WP covers other languages as well. The scoop is

(expression 1) ? expression 2 : expression 3

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If expression 1 evaluates to true, then expression 2 is evaluated.

If expression 1 evaluates to false, then expression 3 is evaluated instead.

Or, to explain that using your own code snippet as an example:

msFrameSpan /= upsampleFPS ? 2 : 1;

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If 'upsampleFPS is non-zero, 'msFrameSpan' will be divided by 2, otherwise it will be divided by 1 - i.e. stay the same. Which also illustrates that this operator can be misused, since a

 if (upsampleFPS) msFrameSpan /= 2;

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would achieve the same, omitting an unnecessary division by 1. Not sure if every compiler is able to optimize that code to leave out that operation.

So as I understand, if I have a boolean

x = upsampleFPS ==true ? false

So when upsampleFPS is true it will be true else false?

That will depend on what type 'upsampleFPS' is. If it is 'bool', 'true' or 'false' are the two options, but an expression in the sense of C/C++ is considered 'true' when it is non-null. 'false' is the equivalent to 'equal to 0'.

upsampleFPS is a simple integer. It contain pal or ntsc.  

So bool x = upsampleFPS==25 ? true: false

So if upsampleFPS is 25 it will set x to true else to false?

Thank you.