Why cout is not printing string which is evaluated by ternary operator

Question

I was writing code using ternary operator instead of if/else to save some time in Competitive Programming. But I was stuck in one case and here is the code

std::cout<< a%2? "string1" : "string2";

OUTPUT on my system: 0 or 1 as per 'a'

Excepted: string1 or string2

I think here ternary operator is returning "const char *" after evaluation, but I'm not getting expected results. So here are my doubts about it.

Why const char * ram = "ram"; std::cout<<ram; works fine but above code don't, to me both seems to have const char * as input to cout, so what is difference between them?
Any workaround to print strings as intended above using ternary operator?

whoever downvoted it could you suggest me how to improve this question, or because I missed the precedence that's why — rkscodes, Mar 06 '21 at 14:00
I didn't downvote, but I have seen this asked way too many times on this website. This maybe why someone downvoted it. — Aykhan Hagverdili, Mar 06 '21 at 14:02
Your question was probably downvoted because it's about C++ basics, other than that it looks well-written to me. — HolyBlackCat, Mar 06 '21 at 14:05
I didn't downvote. The phrase "... Competitive Programming ..." may have been a trigger phrase. — Eljay, Mar 06 '21 at 15:05

songyuanyao · Accepted Answer · 2021-03-06T14:07:09.507

4

operator<< has higher precedence than ternary conditional operator, so std::cout<< a%2? "string1" : "string2"; has the same effect as (std::cout<< a%2) ? "string1" : "string2";. As the result a%2 is printed out instead. (std::cout<< a%2 returns std::cout, which could convert to bool, regardless of the result is true or false, "string1" or "string2" don't have any effect here.)

You should add parentheses like

std::cout<< (a%2? "string1" : "string2");

edited Mar 06 '21 at 14:07

answered Mar 06 '21 at 13:51

songyuanyao

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I got it ; (std::cout< – rkscodes Mar 06 '21 at 13:57
@codeitram `std::cout` could [converto to `bool`](https://en.cppreference.com/w/cpp/io/basic_ios/operator_bool). – songyuanyao Mar 06 '21 at 14:02
2

@codeitram It's equivalent to `std::cout << a%2;` followed by `std::cout ? "string1" : "string2"`. Using `std::cout` in a condition like this returns true if it did not encouter any problems while printing, now or earlier. – HolyBlackCat Mar 06 '21 at 14:04
Got it now @HolyBlackCat – rkscodes Mar 06 '21 at 14:09

Why cout is not printing string which is evaluated by ternary operator

1 Answers1