# Using "not" in compound conditions **URL:** \ **Category:** Ruby\ **Created:** [October 30, 2006, 8:43am UTC](https://www.ruby-forum.com/t/using-not-in-compound-conditions/74102 "2006-10-30T08:43:19Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![jazcyk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e56c9b/32.png) [@jazcyk](https://www.ruby-forum.com/u/jazcyk)\ **Post date:** [October 30, 2006, 8:43am UTC](https://www.ruby-forum.com/t/using-not-in-compound-conditions/74102/1 "2006-10-30T08:43:19Z")
Hi I am still a beginner at Ruby, and have just arrived at this in my learning curve. I would like to code not(condition1) && not(condition2) This is accepted in irb - not(condition1) && condition2 but this produces a syntax error condition1 && not(condition2) I do not get it (obviously). I do not even know what to ask in reply - How do I code a compound condition, without introducing extra wrappers like - (not(condition1)) && (not(condition2)) Regards Peter ---
**Author:** ![jazcyk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e56c9b/32.png) [@jazcyk](https://www.ruby-forum.com/u/jazcyk)\ **Post date:** [November 1, 2006, 9:57pm UTC](https://www.ruby-forum.com/t/using-not-in-compound-conditions/74102/2 "2006-11-01T21:57:58Z")
Peter L. wrote: > Hi > I am still a beginner at Ruby, and have just arrived at this in my > learning curve. > > I would like to code > not(condition1) && not(condition2) > This is accepted in irb - > not(condition1) && condition2 > but this produces a syntax error > condition1 && not(condition2) > > I do not get it (obviously). I do not even know what to ask in reply - > How do I code a compound condition, without introducing extra wrappers > like - > (not(condition1)) && (not(condition2)) I never use the ‘not’ logical negation. I always use ‘!’. There is a difference between ‘not’ and ‘!’; and that is precedence. ‘!’ is higher than ‘&&’ ‘&&’ is higher than ‘not’ ‘not’ is higher than ‘and’ If you mix logical operators so that precedence is not properly maintained, you end up with weird results. In your ‘condition1 && not(condition2)’ case, the ‘&&’ will be acted on first rather than the ‘not’. This results on the right side of the ‘&&’ have yet to be processed which results in the syntax error. As you learned, adding parathesis changes precedence and corrects the problem. The real solution is to not mix logical operators. condition1 && !condition2 or condition1 and not(condition2) both work. ---
**Author:** ![jazcyk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e56c9b/32.png) [@jazcyk](https://www.ruby-forum.com/u/jazcyk)\ **Post date:** [November 7, 2006, 10:44am UTC](https://www.ruby-forum.com/t/using-not-in-compound-conditions/74102/3 "2006-11-07T10:44:46Z")
On 2006.10.30 16:43, Peter L. wrote: > I do not get it (obviously). I do not even know what to ask in reply - > How do I code a compound condition, without introducing extra wrappers > like - > (not(condition1)) && (not(condition2)) Alternatives: (not condition1) and (not condition2) !condition && !condition And my favourite: not (condition1 or condition2) ---
**Author:** ![jazcyk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e56c9b/32.png) [@jazcyk](https://www.ruby-forum.com/u/jazcyk)\ **Post date:** [November 7, 2006, 10:44am UTC](https://www.ruby-forum.com/t/using-not-in-compound-conditions/74102/4 "2006-11-07T10:44:48Z")
Peter L. wrote: > I do not get it (obviously). I do not even know what to ask in reply - > How do I code a compound condition, without introducing extra wrappers > like - > (not(condition1)) && (not(condition2)) > > Regards > Peter “&&”, “||”, and “!” have higher precedence than “and”, “or” and “not” - so it can be tricky. However, you could do: (not condition1) && (not condition2) or, not mixing the two: not condition1 and not condition2 Of course, it’s best to be clear, and parentheses help that. Hope that helps. -Justin ---
**Author:** ![jazcyk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e56c9b/32.png) [@jazcyk](https://www.ruby-forum.com/u/jazcyk)\ **Post date:** [November 2, 2006, 3:21pm UTC](https://www.ruby-forum.com/t/using-not-in-compound-conditions/74102/5 "2006-11-02T15:21:04Z")
Thankyou Dale for pointing me in the right direction. For anybody else looking at precedence, here is a list of the operator precedences - [The Ruby Language](http://phrogz.net/ProgrammingRuby/language.html#table_18.4) ---
**Author:** ![jazcyk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e56c9b/32.png) [@jazcyk](https://www.ruby-forum.com/u/jazcyk)\ **Post date:** [November 7, 2006, 10:47am UTC](https://www.ruby-forum.com/t/using-not-in-compound-conditions/74102/6 "2006-11-07T10:47:03Z")
Peter L. wrote: > I do not get it (obviously). I do not even know what to ask in reply - > How do I code a compound condition, without introducing extra wrappers > like - > (not(condition1)) && (not(condition2)) > > Regards > Peter For compound conditions, I’d use ! instead of not, likewise && and || instead of and and or. With copious parentheses. I prefer the word variants when the result would read like a sentence - with compound booleans all hope is lost anyway, and I prefer to be able to tell terms apart from operators easier (one being letters, the other special characters). Also, due to the low binding of not, I prefer to use “unless” and “until” instead of “if not” and “while not”. Also, I think the (!(condition1) && !(condition2)) is slightly bad form. Inverting the logic makes things simpler to read: (condition1 || condition2). Yay freshman discrete maths. (Although I admit to cheating, I fired up IDEA to tell me this.) David