Problem with compiler logic?

Question

Simple example:
int x=10, y=5;
cout<<y++ + 2<<endl;
cout<<x++ + x;

SoloLearnC++ gives 7 and 21;
Dev-C++ 4.9.9.2 gives 7 and 20;

Problem how the compiler interpret x after operation x++.

int x =10;
x++ + x;
SoloLearnC++ interpret like this:
10 + 11 = 21, x=11;
DevC++ interpret:
10 + 10 = 20, x=11;

Answer 1

"Problem with compiler logic"

Have you heard of "Undefined behavior"?!
These two expressions break the sequencing rule.

y++ + 2
x++ + x

"Modifying an object between two sequence points more than once produces undefined behavior.[...] ¹"

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¹ https://en.wikipedia.org/wiki/Undefined_behavior

Answer 2

So if I play one-on-one with someone, and the system gives me the tasks containing "undefined behavior" like x++ + x, I can just say: bad task. ok)