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Ternary Operators

rcast (354)
Can somebody explain in simple terms how this works and what it produces?
 
 
a = --b ? b : (b = -99);
vlad from moscow (6539)
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 (354)
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 (6539)
Please read description of the ternary operator in any book on C++ or here in documentation.
nedo (83)
that is an short hand if else statement
For exemple:
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if(a == 0)
{
  a++;
}
else
{
  a--;
}

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

in our case that would be the same as
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if(--b) // after the decrement b is diferent then 0
{
  a = b;
}
else
{
 b = -99;
 a = b;
}
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cire (8284)
For x = a ? b : c ;, x = (a ? b : c) ; is equivalent.

It could be rewritten as an if/else:

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


With that in mind the original statement above translates to:

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


Last edited on
rcast (354)
Excellent. Thanks
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