4

I have a doubt in the following scenario (C++):

Say, I have an if condition

if ( a ? b ? c : d : false) { // do something } else { // do something else }

This is my interpretation of how it works:

If a is true, it checks b. Then, - If b is true, the if loop is reduced to if (c) - If b is false, the if loop is reduced to if (d) If a is false, the if loop is reduced to if (false)

Is my understanding correct?
Is using this better or multiple if/else checks?

Improve this question
3
  • 2
    Yes your interpretation is correct. Commented Sep 26, 2013 at 5:34
  • You can remove one ternary operator: if (a && (b ? c : d)) Commented Sep 26, 2013 at 5:41
  • For clarification on operator precedence, see en.cppreference.com/w/cpp/language/operator_precedence. Commented Sep 26, 2013 at 5:45

5 Answers 5

Reset to default
8

Please use this in parenthesis, as it helps improve readability. Also, it is fine using multiple ternary operators. 

if ( a ? (b ? c : d) : false) { // do something } else { // do something else }
Improve this answer
Sign up to request clarification or add additional context in comments.

3 Comments

@mdv:The order of execution changes. But it will give you the end result u need.
Say my check "a" is a pointer validity check, and in "b" I check a data pointed by the pointer. I need to check "b" only if "a" is true, that is, if the pointer is valid. In this case, the order becomes important. How will the code behave with no parenthesis?
The execution order does not change. ?: only evaluates one of the 2nd and 3rd operands, based on the 1st. So the parentheses do not change execution order, just improve readability.
7

Your question is in two parts, firstly about the behavior of the statement, and then about whether you should do this; allow me to show you how many programmers would solve the second.

Imagine it's 4.30am on a Saturday morning and you're hung over and there is a bug in this code, and you need it fixed within the next 30 minutes or your job/business is at risk.

if (a ? b ? c : d : false)

or

if (a) { if (b) return c; else return d; } else { return false; }

or

if (!a) return false; if (!b) return d; return c;

or

if (a) return b ? c : d; else return false;

Which was the right choice?

-- edit --

With single letter variable names, it looks innocent enough. So, some real variable names:

if (application.config.usingUTCTimezone ? system.environment.biosTimezoneIsUTC ? haveNTPServerConfigured : system.time.clockIsSynchronized : false)

or

if (application.config.usingUTCTimezone ? system.environment.biosTimezoneIsUTC ? haveNTPServerConfigured : system.time.clockIsSynchronized : false)

or

if (application.config.usingUTCTimezone) { if (system.environment.biosTimezoneIsUTC) return haveNTPServerConfigured; else return system.time.clockIsSynchronized; } else { return false; }

or

if (!application.config.usingUTCTimezone) return false; if (!system.environment.biosTimezoneIsUTC) return system.time.clockIsSynchronized; return haveNTPServerConfigured;

or

if (application.config.usingUTCTimezone) return system.environment.biosTimezoneIsUTC ? haveNTPServerConfigured : system.time.clockIsSynchronized; else return false;
Improve this answer

4 Comments

Yes! Clarity over brevity.
Uh, other than the first option being the worst, I'm not sure which of the other three are best? Or is your point that any of the latter are better?
seems like the last option is the clear and concise, readability and performance should be higher priorities than minimizing lines of code
@Federico I added samples with real variable names for contrast. Annecdote: golang tackles this by not having the ternary but instead letting you use 'switch' with conditionals producing a rather nice and readable alternative.
3

Is my understanding correct?

Yes, your interpretation is correct.

Is using this better or multiple if/else checks?

As you know the code: 

if ( a ? b ? c : d : false) { "Code-1" } else { "Code-2" }

could be written like: 

if(a){ if(b){ if (c){ "code-1" } else{ "code-2" } } else{ if(d){ "code-1" } else{ "code-2" } } } else{ //then false; "Code-2" }

Now which you will prefer in above two. Second is long and includes many nested level code (hard to understand and bug). Additionally first code that can be improved in readability as: 

if ( a ? (b ? c : d) : false)

as @ManikandanSigamani answered.

As I noted @WhozCraig also give an another technique to write your code better if (a && (b ? c : d)) using && that supports Short-Circuit logic.

A good programmer is one who know one than one technique to solve a problem and also know which is better. A short and linear codding is preferable in general. In small writing small code chances of making mistakes are less (looks like functional programming better then imperative programming). And small code easily can improved as in your case suggested by @ManikandanSigamani and @WhozCraig.

I will prefer: if (a && (b ? c : d)) form!

Improve this answer

Comments

1

Yes, you are correct at stating:

If a is true, it checks b. Then, - If b is true, the if condition is reduced to if (c) - If b is false, the if condition is reduced to if (d) If a is false, the if condition is reduced to if (false)

but if() is not a loop but a condition statement. and writing condition in parenthesis make it more readable.

if ( a ? (b ? c : d) : false)

or you can simplify it:

if ( a && (b ? c : d))
Improve this answer

Comments

0

Though it works, nesting ternary operator like this is seldom readable.

Writing it as 

if ( a && (( b && c ) || d )) { // do something } else { // do something else }

is, imho, much more readable and it is not much longer than your original code.

Improve this answer

Comments

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.