string manipulation with ? and : - where is the reference ?

Using Arduino Programming Questions
1

I saw this in a sample program, but can't find anything in the ref manual about it. Looks really neat, though so would like to use it more, seems to be similar to switch/case.

Serial.println ((optionSwitch & mask) ? "closed" : "open");

2

Yes, you have to find a more complete C++ reference. There are many online.

3

a search for c++ conditional ? : led me to MSDN where all was explained. Thanks. (just had to blunder into the fact that it is a conditional....)

4

It's called -

ternary-operator

5

Call it a conditional expression, the same way you call + addition rather than binary operator.

6

Here is a run down of its uses (its entire usefulness is not well known or covered by other examples): http://arduino.land/FAQ/content/2/27/en/what-does-this-code-do-a-%3D-x-y-z.html

7

OK, what you need is a basic primer on C/C++. Like this one.

There are many, many others. Or you could buy the brown book, although they changed the cover a few years back so it's nowhere near as cool as it used to be. (I learned C from the blue book, back in the day).

In any case, nostalgia aside, the page from that tutorial describing the ternary operator is this one. Look through the whole thing.

8

GordB:
I saw this in a sample program, but can't find anything in the ref manual about it. Looks really neat, though so would like to use it more, seems to be similar to switch/case.

Serial.println ((optionSwitch & mask) ? "closed" : "open");

What that does is simplify an "if" type set of instructions. For example, look at this code example for a hypothetical temperature controller project:

var t = readTempSensor();
if (t > 70) {
    setHeater (0); // hotter than 70, turn heater off
} else {
    setHeater (1); // 70 or less, turn heater on
}

Now we will do the same thing using the ternary operator (the ? and : thing):

var t = readTempSensor();
setHeater ((t > 70) ? 0 : 1); // turn heater off or on

How that operator works is like this:

if THING is TRUE then do THIS otherwise do THAT

In the second code example, "thing" is the statement "t > 70". So if t is indeed greater than 70 (i.e. "true") then we pass the "0" to setHeater, meaning "we are at or above 70, so turn the heater off". If t is less than or equal to 70 (i.e. "false") then we pass the "1" to setHeater.

Another example could be:

RAINING ? USE_UMBRELLA : DON'T_NEED_UMBRELLA;

If "RAINING" is true (i.e. it's wet out) then do what follows the "?", otherwise do what follows the ":".

Make sense?

Hope this helps.