c++ bool concatenation with |= - c++

I'm wondering about the way to concatenate bools.
What I sometimes need is to get a flag whether at least one object in a list of objects has a certain value/state/is focused etc..
What I do is this:
bool bHasState( false );
for ( auto o : MyObjectList )
{
bHasState |= ( o->state() == SOME_STATE );
}
Some of my colleagues always replace this with
bHasState = bHasState || ( o->state() == SOME_STATE );
Is this just a syntactic difference, or is my way wrong, dangerous or slow?

Expanding from the comments: the main difference here is that your version always evaluates the right-hand expression, while the version with || (or the proposed if version, which is essentially the same) doesn't, as || has short-circuit evaluation.1
The performance difference boils down to balancing the cost of a branch (an easily predicted one, since it's going to be always taken until you find an element that makes bHasState true, and then always not taken) with the cost of calling state() on every item, which may be extremely cheap (if it's a straight inline accessor, so the only cost is going to be a potential cache miss) or quite costly (if state() isn't inline, performs more complex calculations or - say - has to acquire a busy mutex).2
Still, if you were to decide that branching at each iteration isn't going to be so costly, probably you should go one step further: just break out of the loop when you find the first item whose state matches what you are looking for
bool bHasState( false );
for ( auto o : MyObjectList ) {
if(o->state() == SOME_STATE) {
bHasState = true;
break;
}
}
as it's true that the || branch is going to be easily predicted, but not looping at all over irrelevant items is surely going to be faster, especially it MyObjectList contains many elements.
Incidentally, the same exact semantic can be reproduced with this horrible standard library one-liner:
bool bHasState = std::any_of(MyObjectList.begin(), MyObjectList.end(),
[](MyObject const& o) { return o->state() == SOME_STATE; });
IOW, it evaluates the right hand expression only if the left hand expression is false; somebody pointed out that, if || is overloaded, it isn't short-circuit anymore, still, here I wouldn't think this is the case - from the context we seem to be dealing with regular integers.
Notice that, if the compiler can prove that calling state() has no observable side-effects (which can be trivially done if it's just an inline getter) it may transform the && to & or the opposite as it prefers, as having or not having the branch isn't technically observable (as far as the C++ standard is concerned).

The replacement is not quite the same. Do please read on:
bHasState |= ( o->state() == SOME_STATE ); is an idiomatic way of switching on a bit if the right hand side is true, or leaving it as it is if the right hand side is false. But it does require the evaluation of o->state(), which if that's expensive, the || alternative might be better.
That said, to me the way you currently have it is perfectly clear. (Personally I'd go one stage further and remove the redundant parentheses, which make the expression appear more complicated than it really is.)
But as a rule of thumb, I also wouldn't fiddle with code that works as you can introduce really subtle bugs. Currently o->state() is always evaluated, it wouldn't be if you changed it to bHasState = bHasState || ( o->state() == SOME_STATE );, bHasState was already true, and || was not overloaded. (Note that || is not short-circuited if || is overloaded.)

Related

Is there anything from the standard library or boost that facilitates conditionally executing a function?

I am refactoring a function with too many if-else's, something like the following but more complicated. Some major characteristics of this function are:
It bails out early for many pre-conditions (e.g., condition1() and condition2()).
It only does some meaningful stuff on very specific scenarios (e.g., doA() and doB()). (Oh yeah, the beauty of temporary bug fixing!)
Some pre-conditions may or may not be independent of additional conditions (e.g., condition3/4/5/6()).
retT foo() { // total complexity count = 6
if (!condition1()) { // complexity +1
return retT{};
}
if (!condition2()) { // complexity +1
return retT{};
}
if (condition3()) { // complexity +1
if (condition4() || condition5()) { // complexity +2
return doA();
}
else if (condition6()) { // complexity +1
return doB();
}
}
return retT{};
}
The goal is to call out those actual works on their precise conditions rather than leaving them vulnerable to the change of the if-else structure in foo(). More specifically, I would like to turn foo() into something like this:
retT foo() { // total complexity count = 4
ConditionalCommand<retT> conditionalDoA{doA};
conditionalDoA.addCondition(condition1());
conditionalDoA.addCondition(condition2());
conditionalDoA.addCondition(condition3());
conditionalDoA.addCondition(condition4() || condition5()); // complexity +1
ConditionalCommand<retT> conditionalDoB{doB};
conditionalDoB.addCondition(condition1());
conditionalDoB.addCondition(condition2());
conditionalDoB.addCondition(condition3());
conditionalDoB.addCondition(!(condition4() || condition5())); // complexity +2
conditionalDoB.addCondition(condition6());
for (auto& do : {conditionalDoA, conditionalDoB}) {
if (do()) { // complexity +1
return do.result();
}
}
return retT{};
}
This makes the implementation more linear and the conditions for performing a particular work more explicit. I understand that it would be equivalent to just creating a first-level if-clause for each work with all the added conditions listed, but the above code would:
reduce our internal complexity measurement (if-else, logical operators, and ternary based, as illustrated in the code comments),
prevent future intrusion into the first-level if-clauses by a new developer, for example, who wants to doC() instead of doA() if condition7() is true, and
allow me to refine each work's conditions independently of those of the other works (recall that some conditions might be depending on each other).
So the question is, is there any existing std or boost utility that does what ConditionalCommand does so I don't need to reinvent the wheel?
Edit: conclusion at the top, frame challenge below.
Back to the original question, is there anything existing in std or boost to do what ConditionalCommand does?
OK, if you're really not worried about the fact that this design violates your own stated requirements, the answer is: NO. Nothing does exactly this.
However, you could just write something like
std::array condA { condition1(), condition2(), condition3(),
(condition4() || condition5()) };
if (std::ranges::all_of(condA, std::identity{})) doA();
if (std::ranges::all_of(
std::initializer_list<bool>{
condition1(), condition2(), condition3(),
(condition4() || condition5()),
condition6()
},
std::identity{})
)
doB();
or whatever takes your fancy. You're only suggesting a very thin convenience layer over this logic.
This makes the implementation more linear
Between perfectly linear control flow and a perfectly linear data structure, I don't really see any advantage either way on this criterion.
the conditions for performing a particular work more explicit
If by "more explicit" you mean "more declarative", then I guess so. You've hidden everything that is actually going on inside some mystery templates though, so it had better be very clear, intuitive and well documented.
reduce our internal complexity measurement (if-else, logical operators, and ternary based, as illustrated in the code comments),
Your "internal complexity measurement" is, frankly, stupid. If you optimize for a bad objective, you'll get a bad result.
Here you have very obviously increased overall complexity, increasing the learning curve for new developers, making the relationship between conditions and their consequences less clear and control flow much harder to debug.
But you've done it in a way that your "internal complexity measurement" chooses to ignore, so it looks like an improvement.
Although I dislike cyclomatic complexity as a broad measure, if yours is genuinely so much higher than shown in the question that refactoring is required - I'd still try just refactoring the procedural code before I considered your proposal.
prevent future intrusion into the first-level if-clauses by a new developer, for example, who wants to doC() instead of doA() if condition7() is true
Just write unit tests for every combination of your 7 conditions (or a single test that runs every permutation) and let your junior developer find out for themselves when the CI server complains about their branch.
You're not helping them get less junior by obfuscating your code like this, you're trying to insulate yourself from their mistakes in a way that doesn't actually help them improve.
Also, the original control flow may even have bugs in them
In that case you should definitely be writing test cases first! You're talking about refactoring code you don't trust in a way that violates your own stated requirements with no way to validate the result.
allow me to refine each work's conditions independently of those of the other works (recall that some conditions might be depending on each other).
If you really want a less error-prone way of organizing this, these condition inter-dependencies should be encoded explicitly. At the moment you can still break everything by adding conditions in the wrong order.
Further, you're currently executing all conditions unconditionally except for the short-circuit evaluation of conditions 4 & 5. Is this even well-defined? Is it guaranteed to remain well-defined?
Still further, you're now evaluating each condition multiple times, once for each possible action.
If you really must encode this in data rather than code, it could be something like an explicit dependency graph (so condition2 depends-on condition1 and is never executed unless that dependency evaluates to true). Then you can have multiple leaf actions attached to the same graph, and don't need any redundant re-evaluations.
To be fair, implementing this is a pain, but at least it satisfies your dependency requirement.
I agree with all the others that your attempt is just hiding complexity under a questionably more readable blanked. I find it much more unreadable than the original.
I think your only hope is to look at the original code and play untangle with it.
In your simplified example you have more return statements than possible returned values, and I bet in the original too, you have far more returns than possible returned values. So why don't you simply make a map (with pen and paper) of what condition leads to what return value?
Taking your simple example,
retT{} is returned only if !c1 || !c2 || !c3 || (!c4 && !c5 && !c6)
doA() is returned only if c1 && c2 && c3 && (c4 || c5)
doB() is returned only if c1 && c2 && c3 && c6
Notice that the first boolean can be re-written, using De Morgan laws, like !(c1 && c2 && c3 && (c4 || c5 || c6)).
Follows the observation that the only important booleans are actually these:
bool b1 = c1 && c2 && c3;
bool b2 = c4 || c5;
bool b3 = c6;
You can then rewrite your logic as
doA() is returned only if b1 && b2, call it p1
doB() is returned only if b1 && b3, call it p2
retT{} is returned only if !(b1 && (b2 || b3)) = !((b1 && b2) || !(b1 && b3)) = !(b1 && b2) && !(b1 && b3) = !p1 && !p2
the last sequence of equalities is the verification that all branches indeed lead to a return (otherwise the code would be erroneous).
With the above in mind (and on paper) the code can be simplified like this:
bool b1 = c1 && c2 && c3;
bool b2 = c4 || c5;
bool b3 = c6;
if (b1) {
if (b2) {
return doA();
}
if (b3) {
return doB();
}
}
return retT{};
or, if you are really scared about the time needed to compute the booleans, you can compute than "lazily":
bool b1 = c1 && c2 && c3;
if (b1) {
bool b2 = c4 || c5;
if (b2) {
return doA();
}
//bool b3 = c6;
if (/*b3*/c6) {
return doB();
}
}
return retT{};

Else keyword in non void function in C++ [duplicate]

I am always in the habit of using if, else-if statement instead of multiple if statements.
Example:
int val = -1;
if (a == b1) {
return c1;
} else if (a == b2) {
return c2;
} ...
...
} else {
return c11;
}
How does it compare to example 2:
if (a == b1) {
return c1;
}
if (a == b2) {
return c2;
}
....
if (a == b11) {
return c11;
}
I know functionality wise they are the same. But is it best practice to do if else-if, or not? It's raised by one of my friends when I pointed out he could structure the code base differently to make it cleaner. It's already a habit for me for long but I have never asked why.
if-elseif-else statements stop doing comparisons as soon as it finds one that's true. if-if-if does every comparison. The first is more efficient.
Edit: It's been pointed out in comments that you do a return within each if block. In these cases, or in cases where control will leave the method (exceptions), there is no difference between doing multiple if statements and doing if-elseif-else statements.
However, it's best practice to use if-elseif-else anyhow. Suppose you change your code such that you don't do a return in every if block. Then, to remain efficient, you'd also have to change to an if-elseif-else idiom. Having it be if-elseif-else from the beginning saves you edits in the future, and is clearer to people reading your code (witness the misinterpretation I just gave you by doing a skim-over of your code!).
What about the case where b1 == b2? (And if a == b1 and a == b2?)
When that happens, generally speaking, the following two chunks of code will very likely have different behavior:
if (a == b1) {
/* do stuff here, and break out of the test */
}
else if (a == b2) {
/* this block is never reached */
}
and:
if (a == b1) {
/* do stuff here */
}
if (a == b2) {
/* do this stuff, as well */
}
If you want to clearly delineate functionality for the different cases, use if-else or switch-case to make one test.
If you want different functionality for multiple cases, then use multiple if blocks as separate tests.
It's not a question of "best practices" so much as defining whether you have one test or multiple tests.
The are NOT functionally equivalent.
The only way it would be functionally equivalent is if you did an "if" statement for every single possible value of a (ie: every possibly int value, as defined in limits.h in C; using INT_MIN and INT_MAX, or equivalent in Java).
The else statement allows you to cover every possible remaining value without having to write millions of "if" statements.
Also, it's better coding practice to use if...else if...else, just like how in a switch/case statement, your compiler will nag you with a warning if you don't provide a "default" case statement. This prevents you from overlooking invalid values in your program. eg:
double square_root(double x) {
if(x > 0.0f) {
return sqrt(x);
} else if(x == 0.0f) {
return x;
} else {
printf("INVALID VALUE: x must be greater than zero");
return 0.0f;
}
}
Do you want to type millions of if statements for each possible value of x in this case? Doubt it :)
Cheers!
This totally depends on the condition you're testing. In your example it will make no difference eventually but as best practice, if you want ONE of the conditions to be eventually executed then you better use if else
if (x > 1) {
System.out.println("Hello!");
}else if (x < 1) {
System.out.println("Bye!");
}
Also note that if the first condition is TRUE the second will NOT be checked at all but if you use
if (x > 1) {
System.out.println("Hello!");
}
if (x < 1) {
System.out.println("Bye!");
}
The second condition will be checked even if the first condition is TRUE. This might be resolved by the optimizer eventually but as far as I know it behaves that way. Also the first one is the one is meant to be written and behaves like this so it is always the best choice for me unless the logic requires otherwise.
if and else if is different to two consecutive if statements. In the first, when the CPU takes the first if branch the else if won't be checked. In the two consecutive if statements, even if the the first if is checked and taken, the next if will also be check and take if the the condition is true.
I tend to think that using else if is easier more robust in the face of code changes. If someone were to adjust the control flow of the function and replaces a return with side-effect or a function call with a try-catch the else-if would fail hard if all conditions are truly exclusive. It really depends to much on the exact code you are working with to make a general judgment and you need to consider the possible trade-offs with brevity.
With return statements in each if branch.
In your code, you have return statements in each of the if conditions. When you have a situation like this, there are two ways to write this. The first is how you've written it in Example 1:
if (a == b1) {
return c1;
} else if (a == b2) {
return c2;
} else {
return c11;
}
The other is as follows:
if (a == b1) {
return c1;
}
if (a == b2) {
return c2;
}
return c11; // no if or else around this return statement
These two ways of writing your code are identical.
The way you wrote your code in example 2 wouldn't compile in C++ or Java (and would be undefined behavior in C), because the compiler doesn't know that you've covered all possible values of a so it thinks there's a code path through the function that can get you to the end of the function without returning a return value.
if (a == b1) {
return c1;
}
if (a == b2) {
return c2;
}
...
if (a == b11) {
return c11;
}
// what if you set a to some value c12?
Without return statements in each if branch.
Without return statements in each if branch, your code would be functionally identical only if the following statements are true:
You don't mutate the value of a in any of the if branches.
== is an equivalence relation (in the mathematical sense) and none of the b1 thru b11 are in the same equivalence class.
== doesn't have any side effects.
To clarify further about point #2 (and also point #3):
== is always an equivalence relation in C or Java and never has side effects.
In languages that let you override the == operator, such as C++, Ruby, or Scala, the overridden == operator may not be an equivalence relation, and it may have side effects. We certainly hope that whoever overrides the == operator was sane enough to write an equivalence relation that doesn't have side effects, but there's no guarantee.
In JavaScript and certain other programming languages with loose type conversion rules, there are cases built into the language where == is not transitive, or not symmetric. (In Javascript, === is an equivalence relation.)
In terms of performance, example #1 is guaranteed not to perform any comparisons after the one that matches. It may be possible for the compiler to optimize #2 to skip the extra comparisons, but it's unlikely. In the following example, it probably can't, and if the strings are long, the extra comparisons aren't cheap.
if (strcmp(str, "b1") == 0) {
...
}
if (strcmp(str, "b2") == 0) {
...
}
if (strcmp(str, "b3") == 0) {
...
}
I prefer if/else structures, because it's much easier to evaluate all possible states of your problem in every variation together with switches. It's more robust I find and quicker to debug especially when you do multiple Boolean evaluations in a weak-typed environment such as PHP, example why elseif is bad (exaggerated for demonstration):
if(a && (c == d))
{
} elseif ( b && (!d || a))
{
} elseif ( d == a && ( b^2 > c))
{
} else {
}
This problem has beyond 4^2=16 boolean states, which is simply to demonstrate the weak-typing effects that makes things even worse. It isn't so hard to imagine a three state variable, three variable problem involved in a if ab elseif bc type of way.
Leave optimization to the compiler.
In most cases, using if-elseif-else and switch statements over if-if-if statements is more efficient (since it makes it easier for the compiler to create jump/lookup tables) and better practice since it makes your code more readable, plus the compiler makes sure you include a default case in the switch. This answer, along with this table comparing the three different statements was synthesized using other answer posts on this page as well as those of a similar SO question.
I think these code snippets are equivalent for the simple reason that you have many return statements. If you had a single return statements, you would be using else constructs that here are unnecessary.
Your comparison relies on the fact that the body of the if statements return control from the method. Otherwise, the functionality would be different.
In this case, they perform the same functionality. The latter is much easier to read and understand in my opinion and would be my choice as which to use.
They potentially do different things.
If a is equal to b1 and b2, you enter two if blocks. In the first example, you only ever enter one. I imagine the first example is faster as the compiler probably does have to check each condition sequentially as certain comparison rules may apply to the object. It may be able to optimise them out... but if you only want one to be entered, the first approach is more obvious, less likely to lead to developer mistake or inefficient code, so I'd definitely recommend that.
CanSpice's answer is correct. An additional consideration for performance is to find out which conditional occurs most often. For example, if a==b1 only occurs 1% of the time, then you get better performance by checking the other case first.
Gir Loves Tacos answer is also good. Best practice is to ensure you have all cases covered.

Nested if statements vs extra else if?

I come across a lot of logic work where I'm not sure what design pattern is better for if statements. In these situations, I can usually put in a nested if statement, or alternatively. These two cases are shown below. What are the pros and cons of both, is there a standard I should follow?
if (val > 0 && is_on)
{
// (1)
}
else if (val > 0)
{
// (2)
}
else
{
// (3)
}
if (val > 0)
{
if(is_on)
{
// same as (1)
}
else
{
// same as (2)
}
}
else
{
// same as (3)
}
I don't think there is any specific pros or cons to any of the approach. Its all depends upon how you want to design your code and what you think is more readable to anyone who is looking at your code for the first time.
As per me, the first approach looks better as its more readable and contains fewer lines of code.
The first approach is more readable. But as the logic expressions (e.g. "val > 0 && is_on") get longer, it starts to make more sense to merge towards the second approach. The second one is easier to debug, so you could start there and then merge back. I'd match the style of the surrounding code/"code-policy" ultimately.
While the other answers are absolutely right in that your primary focus should be be readability, I want to address another difference: execution performance.
In the first example, there are 2 conditions that need evaluated before the else branch can run. If as we scale the number of conditions baked into this else/if ladder, the amount of evaluation to get to the else branch grows linearly. Now, we aren't expecting to have ten thousand conditions or anything, but it is something to take note of nonetheless.
Now, in your second example, we check the common condition between the first two branches, and if that fails, we quick-fail to the else branch, with no extra tests. In the extreme case, this can somewhat resemble a binary search for the correct code block- branching left and right until it finds its match, as opposed to a linear scan that checks each in order one-by-one.
Now, does this mean you should use the latter? Not necessarily- readability is more important, and if you're writing in a compiled language, the compiler will likely optimize away all that away anyways. And even if you're in an interpreted language, the performance hit is probably going to be negligible compared to everything else anyways, unless this is the hot section of a hot loop.
However, if you are bothered by the "wastefulness" of the repetition in the first example, but would rather avoid huge amounts of nesting, often languages will provide an assignment expression syntax, giving you a 3rd option, where you compute the result once and store it to a variable inline, for reuse in subsequent code.
For example:
if (expensive_func1() > 0 && is_on)
{
// (1)
}
else if (expensive_func1() > 0 && expensive_func2() > 0)
{
// (2)
}
else
{
// (3)
}
Becomes:
if ((is_alive = expensive_func1() > 0) && is_on)
{
// (1)
}
else if (is_alive && expensive_func2() > 0)
{
// (2)
}
else
{
// (3)
}
This saves us from recomputing the common sub expressions between our conditionals, in languages were we can't rely on a compiler to do that for us. Sure, we could just assign these to variables explicitly before the if statements, but then we bite the bullet of evaluating all shared expressions, rather than lazily evaluating them as needed (imagine we compute expensive_func2 > 0 for reuse in a 3rd if/else, only to find out we didn't need it, that we're taking the first branch).

Using nested if statements vs logical operator && in c++

Let us say I have an integer array representing the chess pieces on a board;
int board[8][8];
In my chess game, I am currently coding a generator function that will return an integer vector of all legal moves.
Naturally, I will be using if statements
I am at a point where I need to check a certain element in the board relative to a piece on the board
For example, If I have a pawn piece;
board[row][col] == 'p';
I need to generate [row+1][col], [row+2][col] and in some cases if it can attack a piece, a change in column too.
But if a piece is on any edge of the board, board[row+1][col] will return be index out of range
For that reason I need an extra if statement.
My question is, shall i use:
if (pieceisnotonedge && board[row+1][col] == 0)
or
if (pieceisnotonedge)
{
if (board[row+1][col] == 0)
}
For the first example, if pieceisnotonedge returns false, will it also check the next condition? Because if it does, then I am in trouble.
For the first example, if pieceisnotonedge returns false, will it also
check the next condition?
No, it will not. Because the build-in logical operators do short-circuiting. From cppreference.com:
Builtin operators && and || perform short-circuit evaluation (do not
evaluate the second operand if the result is known after evaluating
the first), but overloaded operators behave like a regular function
calls and always evaluate both operands
Therefore, in
if (pieceisnotonedge && board[row+1][col] == 0)
if the pieceisnotonedge is false, the second will not be evaluated. Therefore, having a nested ifs is redundant, and you can go with the first version.
For the first example, if pieceisnotonedge returns false, will it also check the next condition?
No. It will "short-circuit" because if the first condition is false, checking the conditions after it is unnecessary. Read more here and here.
This is guranteed by the C++ standard:
7.6.14
... && guarantees left-to-right evaluation: the second operand is not evaluated if the first operand is false.
Note that, for || this is opposite, that is, if the first condition is "true", then checking the conditions afterwards is unnecessary
Shall i use; or...
Both are same, if you have a short if statement (with only two conditions), I would suggest using the first approach. In terms of efficiency there is no difference and you can verify this by looking at the generated assembly for both cases on godbolt
For the shown code there is no difference, both board[row+1][col] == 0 are only evaluated if pieceisnotonedge is true.
If you should use one or the other, cannot be said be in general, as it depends on other factors (like semantic, readability, …) too.
If you e.g. want to have an action that it done if either pieceisnotonedge or board[row+1][col] == 0 is false, then you probably would use &&, because then you can write:
if (pieceisnotonedge && board[row+1][col] == 0) {
} else {
// do something else
}
with your other style you would need to write:
if (pieceisnotonedge){
if (board[row+1][col] == 0) {
// do something else
}
} else {
// do something else
}
In general, your first aim should be to have readable code. While pieceisnotonedge && board[row+1][col] == 0 easy to read, more complex expressions might not be. So you would decide that on a case by case basis, if you want to use one expression or multiple if.
For the first example, if pieceisnotonedge returns false, will it also check the next condition?
No. It will stop immediately after pieceisnotonedge is evaluated to false. There is no subsequent check for the remainder condition board[row+1][col] == 0
You can use nested if as the second code as well - no difference. It's just a matter of what code would look clearer.

Conditional Operator: How much flexibility?

I would like to perform the following:
if(x == true)
{
// do this on behalf of x
// do this on behalf of x
// do this on behalf of x
}
Using a conditional operator, is this correct?
x == true ? { /*do a*/, /*do b*/, /*do c*/ } : y == true ? ... ;
Is this malformed?
I am not nesting more than one level with a conditional operator.
The expressions I intend to use are highly terse and simple making a conditional operator, in my opinion, worth using.
P.S. I am not asking A. Which I should use? B. Which is better C. Which is more appropriate
P.S. I am asking how to convert an if-else statement to a ternary conditional operator.
Any advice given on this question regarding coding standards etc. are simply undesired.
Don't compare booleans to true and false. There's no point because they're true or false already! Just write
if (x)
{
// do this on behalf of x
// do this on behalf of x
// do this on behalf of x
}
Your second example doesn't compile because you use { and }. But this might
x ? ( /*do a*/, /*do b*/, /*do c*/ ) : y ? ... ;
but it does depend on what /*do a*/ etc are.
Using comma operator to string different expressions together is within the rules of the language, but it makes the code harder to read (because you have to spot the comma, which isn't always easy, especially if the expression isn't really simple.
The other factor is of course that you can ONLY do this for if (x) ... else if(y) ... type conditionals state.
Sometimes, it seems like people prefer "short code" from "readable code", which is of course great if you are in a competition of "who can write this in the fewest lines", but for everything else, particularly code that "on show" or shared with colleagues that also need to understand it - once a software project gets sufficiently large, it usually becomes hard to understand how the code works WITHOUT obfuscation that makes the code harder to read. I don't really see any benefit in using conditional statements in the way your second example described. It is possible that the example is bad, but generally, I'd say "don't do that".
Of course it works (with C++11). I have not tried a solution but following Herb Sutters way you can use ether a function call or a lambda which is immediately executed:
cond ?
[&]{
int i = some_default_value;
if(someConditionIstrue)
{
Do some operations ancalculate the value of i;
i = some calculated value;
}
return i;
} ()
:
somefun() ;
I have not tried to compile it but here you have an result whih is either computed with an lambda or an normal function.