Ternary Operators

rcast (42)

Can somebody explain in simple terms how this works and what it produces?

a = --b ? b : (b = -99);

vlad from moscow (3662)
At first expression --b is executed. If the result is not equal to zero then the result is assigned to a. Otherwise -99 is assigned to b and to a. You can check this yourself by writing a simple test program.
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rcast (42)
Ok, this is good - I see how -99 can be assigned to ' b', but how does 'a' get assigned too? Isn't 'a' only assigned to the operand on the right of the operator, --b? And what is that second b after the '?' for? finally, how do you get "is not equal to 0"? Is this because this ternary operator tests for true or false?
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vlad from moscow (3662)
Please read description of the ternary operator in any book on C++ or here in documentation.

nedo (31)

that is an short hand if else statement
For exemple:

if(a == 0)
{
  a++;
}
else
{
  a--;
}

is the same thing to
(a == 0) ? a++ : a--;

in our case that would be the same as

if(--b) // after the decrement b is diferent then 0
{
  a = b;
}
else
{
 b = -99;
 a = b;
}

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cire (2347)

For x = a ? b : c ;, x = (a ? b : c) ; is equivalent.

It could be rewritten as an if/else:

if ( x )
   a = b ;
else
   a = c ;

With that in mind the original statement above translates to:

if ( --b )
    a = b ;
else
    a = b = -99 ;

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