int i=20; cout<<i<<i++<<++i

Question

why is the output 22 21 21

Answer 1

In SL Answer will be 202022
it will depend upon compiler...
https://code.sololearn.com/csddmCpnjkqf/?ref=app

Answer 2

i=20

it will first output 20
i++ : one would expect to increment i, and actually it does increment, but only after it writes down i (because the increment operator comes afterwards i++). therefore it writes again 20. and then increments it to 21.
++i : this time the increment takes place before output. so 21 becomes 22.

final output:
20 20 22
and as there is no space between the outputs:
202022

Answer 3

Undefined behaviour.
G++ 6.3.0 outputs 22 21 22
Clang 5.0.0 outputs 20 20 21
And whatever Compiler Hari used outputs 22 21 21.
So out of 3 compilers we get 3 different outputs.

And the moral of this story:
Don't use multiple increment or decrement operators in the same sequences.

Answer 4

https://www.jdoodle.com/online-compiler-c++
Test the code here. 3 compilers available, 2 different results.