Why are multiple statements in ternary operator not executed

2018-06-26 04:21:08

This question already has an answer here:

Undefined behavior and sequence points 4 answers

What's the precedence of comma operator inside conditional operator in C++? 3 answers

Because of operators priority. Your expression evaluates as

((a) ? (nb++, nb2++) : nb--), nb2--;

Operator , ( comma ) is the last thing to process. And this example would not compile at all but

The expression in the middle of the conditional operator (between ? and :) is parsed as if parenthesized.

See C++ Operator Precedence for details.

It's expected behaviour.

Your expression is understood by the compiler as:

((a) ? (nb++, nb2++) : nb--), nb2--;

For more details see:

Something we found when using comma in condition ternary operator?

https://en.wikipedia.org/wiki/Comma_operator

use paranthesis:

a ? (nb++, nb2++) : (nb--, nb2--);

reason: lexical analysis

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