What does ?false:true do/mean?

[Angelo Tan]

?false:true
?true:false

I've encountered this piece of code many times already. I'm wondering what is it for? What does it do? And when should i use it?

[Stephan van Hulst]

Never, because they are pretty useless.

This is called the ternary operator. It consists of a boolean expression, followed by ?, followed by an expression, followed by :, and finally another expression.

If the boolean expression before the question mark evaluates to true, the operator returns the expression after the question mark. Otherwise, it returns the expression after the colon.
Here is an example:

int a = 10;
int b = 20;
int max = a > b ? a : b;

This piece of code assigns to max either a or b, whichever is larger. The ternary operator has its uses. The reason your examples shouldn't be used, is because they simply return the outcome of the boolean expression before the question mark, or its inverse.

[Jesper de Jong]

A line like this:

result = expression ? a : b;

means exactly the same as this:

if (expression) {
  result = a;
}
else {
  result = b;
}

It's just a shorter syntax to write.

As Stephan noted, using "true" and "false" (or "false" and "true") for a and b is pretty useless...

// This is unnecessarily complex...
result = expression ? true : false;

// ... because it is exactly the same as:
result = expression;

// And this is also unnecessarily complex...
result = expression ? false : true;

// ... because it is exactly the same as:
result = !expression;

[Angelo Tan]

thanks for the clear and thorough explanation.

got it now.