Solved:: Ternary Operator - Can I do this?

Question

0.00/5 (No votes)

See more:

I've googled around and have not found documentation of this particular syntax.

Consider the following:

If m_iPage is indeed 7 then StartLight gets set to 1 and EndLight gets set to 4 as desired.
However if m_iPage is say, 0, the StartLight gets set to 0 but EndLight is set to 4, where I
really needed EndLight to be set to 0 also.

(m_iPage != 7) ? StartLight = m_iPage, EndLight = m_iPage : StartLight = 1, EndLight = 4;

This is not correct?

Thanks for the help in advance

Posted 2-Mar-13 5:53am

Ron Anders

Updated 2-Mar-13 6:19am

v3

Add a Solution

Comments

Philippe Mori 5-Mar-13 23:21pm

To understand why it does not works, you have to search information on comma operator and operator precedence instead of ternary operator. Since comma operator has less priority, last part of your expression is always executed as it is not part of the ternary expression.

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Ian A Davidson · Accepted Answer · 2013-03-02T06:35:00

Solution 2

While ProgramFOX's answer is correct, it is precisely this sort of problem where it would be recommended to stick with an if/else statement. It will make the code easier to read and understand what you are doing, both for yourself when you come back to it later, as well as another developer if they have to take the work on.

Furthermore, whether you take that advice or not, you really would be better off having your condition in the positive form (since you are doing something in both cases) because "if this, do x, otherwise do y" is always easier logic to follow than "if not this, do x, otherwise do y".

I.e.

C++

(m_iPage == 7) ? (StartLight = 1, EndLight = 4) : (StartLight = m_iPage, EndLight = m_iPage);

But I repeat, you really should look to change this, if possible, to:

C++

if (m_iPage == 7)
{
   StartLight = 1;
   EndLight = 4;
}
else
{
   StartLight = m_iPage;
   EndLight = m_iPage;
}

Regards,
Ian.

Posted 2-Mar-13 6:35am

Ian A Davidson

Comments

Thomas Daniels 2-Mar-13 12:40pm

I agree, +5!

Ron Anders 2-Mar-13 12:45pm

But if then else is so much less sexy :-)

Philippe Mori 5-Mar-13 22:45pm

You should never use ternary operator for multiple statements but only for simple expressions and generally, you don't want to do any assignment on the right side of the ?.

Ian A Davidson 2-Mar-13 12:58pm

When you have been a software engineer as long as I have, you know the purpose isn't to write "sexy" code.
The best code is code that is maintainable.
There are places where the ternary operator is useful, but it would normally be for the simplest of cases. (One example, off the top of my head, may be to decide what value to pass to a base class in the constructor of an object). In your case, go with if/else. You would have saved yourself a lot of time already, and you'll save yourself a lot of pain later. (E.g. what if later you find you need to do something else when m_iPage is/is not 7 - you'd probably have to change to if/else anyway. Or what if you decide you also need to do something when m_iPage is 6, etc).
Regards,
Ian.

JayantaChatterjee 2-Mar-13 13:23pm

My 5!

Thomas Daniels · Accepted Answer · 2013-03-02T06:07:00

Solution 1

Hi,

You have to write parentheses:

C++

(m_iPage != 7) ? (StartLight = m_iPage, EndLight = m_iPage) : (StartLight = 1, EndLight = 4);

Hope this helps.

Posted 2-Mar-13 6:07am

Thomas Daniels

Comments

Ron Anders 2-Mar-13 12:20pm

Yep, that did it. Thanks ProgramFOX!

Thomas Daniels 2-Mar-13 12:21pm

You're welcome!