Edit - Software Engineering Stack Exchange

You are not logged in. Your edit will be placed in a queue until it is peer reviewed.

We welcome edits that make the post easier to understand and more valuable for readers. Because community members review edits, please try to make the post substantially better than how you found it, for example, by fixing grammar or adding additional resources and hyperlinks.

Required fields*

Rev

Required fields*

Should I fully parenthesize expressions or rely on precedence rules?

Let's say I have a boolean condition a AND b OR c AND d and I'm using a language where AND has a higher order of operation precedence than OR. I could write this line of code:

If (a AND b) OR (c AND d) Then ...

But really, that's equivalent to:

If a AND b OR c AND d Then ...

Are there compelling arguments in favor or against including the extraneous parentheses?
Does practical experience suggest that including them significantly improves readability?
Or is wanting them a sign that a developer really needs to sit down and become conversant in the basics of their language?

Answer*

General case
--

In C#, multiplication and division has a precedence over addition and subtraction.

Still, StyleCop, a tool which enforces common style across the codebase with an additional goal to mitigate the risk of bugs introducing by code which may not be clear enough, has the [rule SA1407][1]. This rule will produce a warning with a piece of code like this:

    var a = 1 + 2 * 3;

It's clear that the result is `7` and not `9`, but still, StyleCop suggests to put parenthesis:

    var a = 1 + (2 * 3);

Your particular case
--

In your particular case, there is a precedence of AND compared to OR in the particular language you use.

**This is not how every language behave. Many others treat AND and OR equally.**

As a developer who works mostly with C#, when I saw your question the first time and read the piece of code without reading what you've wrote before, my first temptation was to comment that the two expressions are not the same. Hopefully, I've read the whole question entirely before commenting.

This particularity and the risk that some developers may believe that AND and OR have the same priority makes it even more important to add parenthesis.

**Don't write code with a goal to show that you're smart. Write code with a goal of readability, including by people who may not be familiar with every aspect of the language.**

  [1]: http://stylecop.soyuz5.com/SA1407.html

Edit Summary*

Cancel

2

"This is very uncommon": According to Stroustrup2013, C++11 seems to have different precedence of AND and OR (p. 257). Same for Python: docs.python.org/2/reference/expressions.html
– Dirk
Commented Jun 11, 2013 at 19:26
12

Re: "Every language I know treat AND and OR equally": I doubt that's true. If it is true, then you don't know any of the ten most popular languages (C, Java, C++, PHP, JavaScript, Python, C#, Perl, SQL, and Ruby), and are in no position to be commenting on what is "uncommon", let alone "very uncommon".
– ruakh
Commented Jun 11, 2013 at 19:34
1

I agree with ruakh and looked it up for C++11, python, matlab and java.
– Dirk
Commented Jun 11, 2013 at 19:36
3

Languages in which AND and OR are binary operators, and which do not treat AND as having a higher precedence than OR, are braindamaged crap whose authors are computer science flunkies. This comes from logic notation. Hello, does "sum of products" not mean anything? There is even a boolean notation which uses multiplication (juxtaposition of factors) for AND, and the + symbol for OR.
– Kaz
Commented Jun 12, 2013 at 7:53
3

@ruakh You just made my point for me. Because there are a handful of pathological edge cases doesn't mean that you shouldn't learn standard Boolean precedence and assume it holds until proven otherwise. We're not talking about arbitrary design decisions here; Boolean algebra was invented long before computers. Also, show me the Pascal spec you're talking about. Here and here show AND before OR.
– dodgethesteamroller
Commented Jun 12, 2013 at 19:51

| Show 6 more comments

Correct minor typos or mistakes
Clarify meaning without changing it
Add related resources or links
Always respect the author’s intent
Don’t use edits to reply to the author

create code fences with backticks ` or tildes ~
```
like so
```
add language identifier to highlight code
```python
def function(foo):
print(foo)
```
put returns between paragraphs
for linebreak add 2 spaces at end
_italic_ or **bold**
indent code by 4 spaces
backtick escapes `like _so_`
quote by placing > at start of line
to make links (use https whenever possible)

<https://example.com>

[example](https://example.com)

<a href="https://example.com">example</a>

formatting help »
answering help »