"DHT11 ? 0 : -40;" What does this syntax mean and what is it called?

Question

return model == DHT11 ? 0 : -40;

I believe it means "return model if between 0 and -40", but I'd like a definitive answer.

Answer 1

Its the ternary operator, equivalent to:

if (model == DHT11)
    return 0;
else
    return -40;

so it has nothing to do with a check for a range.

The ternary operator yields a value, i.e. you could also use this in an assignment like:

retval = model == DHT11 ? 0 : 40;
return retval;

Answer 2

This operator (E1?E2:E3) is called ternary operator, where E are expressions.

It means : "If E1 is true, return E2, else, return E3"

Here's a link to cppreference explaning a bit more.

Answer 3

As already mentioned, it is called the ternary operator.

The ternary operator checks to see if something is true, and if it is, yields the value before the :. If it is false, it yields the value after the :.

In this situation, it checks to see if model == DHT11 evaluates to true, and gives 0 if so. If model == DHT11 evaluates to false, it gives -40. The value the ternary evaluates to is then given to return, quitting the function, and returning either 0 or -40.

Other example:

std::string hi = "hi";
std::cout << (hi == "hi") ? "string hi contains \"hi\"." : "string hi does not contain \"hi\"." << "\n";

Would print:

string hi contains "hi".

General Syntax:

bool ? value1 : value2

The ternary operator is just like an if-else statement, compacted down to one line.