SHshagie·Sep 14, 2024
https://www.wolframalpha.com/input?i=-3%5E2
https://en.wikipedia.org/wiki/Order_of_operations
Parentheses, Exponentiation, Multiplication, Division, Addition, Subtraction
-3^2 would then be correctly parsed as -(3^2) which is -9.
Parsing it as (-3)^2 would require the addition of parentheses.
This gets to the special case of the unary minus sign... which the Wikipedia article specifically calls out.
Special cases
Unary minus sign
There are differing conventions concerning the unary operation '−' (usually pronounced "minus"). In written or printed mathematics, the expression −3² is interpreted to mean −(3²) = −9.
In some applications and programming languages, notably Microsoft Excel, PlanMaker (and other spreadsheet applications) and the programming language bc, unary operations have a higher priority than binary operat
Read the rest
ions, that is, the unary minus has higher precedence than exponentiation, so in those languages −3² will be interpreted as (−3)² = 9. This does not apply to the binary minus operation '−'; for example in Microsoft Excel while the formulas =-2^2, =-(2)^2 and =0+-2^2 return 4, the formulas =0-2^2 and =-(2^2) return −4.
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Digging into this a little bit more...
https://www.gnu.org/software/bc/manual/html_mono/bc.html#TOC...
The expression precedence is as follows: (lowest to highest)
|| operator, left associative
&& operator, left associative
! operator, nonassociative
Relational operators, left associative
Assignment operator, right associative
+ and - operators, left associative
*, / and % operators, left associative
^ operator, right associative
unary - operator, nonassociative
++ and -- operators, nonassociative
This precedence was chosen so that POSIX compliant bc programs will run correctly. This will cause the use of the relational and logical operators to have some unusual behavior when used with assignment expressions. Consider the expression:
...
This brings us to the POSIX specification for bc https://pubs.opengroup.org/onlinepubs/9699919799.2018edition...
This also shows the unary - having higher precedence than ^.
https://github.com/gavinhoward/bc/blob/master/manuals/develo...
This document is meant for the day when I (Gavin D. Howard) get hit by a bus. In other words, it's meant to make the bus factor a non-issue.
This document is supposed to contain all of the knowledge necessary to develop bc and dc.
In addition, this document is meant to add to the oral tradition of software engineering, as described by Bryan Cantrill.
... now, it would be interesting if gavinhoward could clarify some of the design thoughts there (and I absolutely love the oral tradition talk).