Can I use the result of a comparison as an integer in C++?

Question

Can I directly use a comparison as an integer in C++?

For example, can I do this?

int var = 0;
for (i=0;i<20;i++){
    var += (int)(var < 10);
}

In theory, this will increase var up to a value of 10. I know that it works in Python.

Just to make the code more readable, I suggest using `var += (var < 10);`. — R Sahu, Jul 20 '17 at 23:45
@uzumaki, for most people, it is easier to try that simple piece of code than asking a question at SO. — R Sahu, Jul 20 '17 at 23:46
@uzumaki if you're not willing to put in any effort, why should anyone else? — xaxxon, Jul 20 '17 at 23:47
@RSahu The code will work but they won't necessarily understand why. — Captain Obvlious, Jul 20 '17 at 23:48
@CaptainObvlious, that was my response to the OP's comment that *it's eaasier to ask than to compile code*. — R Sahu, Jul 20 '17 at 23:49
You can also write `if (var < 10) ++var;` and nobody has to ask if it works. — Bo Persson, Jul 21 '17 at 01:30

score 1 · Accepted Answer · answered Jul 20 '17 at 23:47

1

Yes, C++ has implicit casting from bool to int.

However, I would suggest you make this a bit more clear that this is your actual intention, so that future readers understand your intent. Explicitly cast it to an int first.

int var = 0;
for (i = 0; i < 20; i++) {
    var += (int)(var < 10);
}

answered Jul 20 '17 at 23:47

Software2

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why not make it even more explicit and use an if statement? – xaxxon Jul 20 '17 at 23:54
It can potentially be slower. An if statement is a potential branching code point. Modern processors may attempt branch prediction. Simply explicitly casting the intended type will produce the same compiled code as the implicit cast, however. Of course, it's an absolutely minimal optimization. If your audience would better understand your code with a few extra if statements, I'd always go for the more readable/understandable code. – Software2 Jul 20 '17 at 23:56
In this case, it seems the if statement is faster since the compiler can know to abandon the loop when var becomes greater than 10. https://godbolt.org/g/PZ1jDn In the code as written in the answer, it always performs 20 iterations. – xaxxon Jul 21 '17 at 04:20

Can I use the result of a comparison as an integer in C++?

1 Answers1