Why x < y < z is bad practice?

Question

People discourage to make if statement like (x < y < z) because its not valid. After i try myself on sololearn, surprisingly it works but with warning. I wonder why it works on sololearn and why people discourage to use this kind of statement. Makes me wonder how x < y < z works?

Answer 1

4 < 5 < 2 is true aka 1
What the computer sees:

(4 < 5) < 2
= (1) < 2
= 1 aka true

It's comparing the "boolean" with an integer.
(The boolean is actually an integer 0 or 1)

Answer 2

Do not chain relational operators like that in languages that are not strongly typed and where the Boolean result of the first operation can be directly compared with a numerical operand of the second operator.

Answer 3

it’s better to separate. If you do it, you may get error. the best way is always to make the condition one by one:
❌ if( a < b < c){}
✅ if( b>a && b<c){}