I read some legacy code:

    if ( 1 || !Foo() )

Is there any seen reason why not to write:

    if ( !Foo() )


Is there any reason for using if(1 || !Foo())?

I have a couple of variables and I want to check the following condition (written out in words, then my failed attempt at bash scripting):

    if varA EQUALS 1 AND ( varB EQUALS &quot;t1&quot; OR varB EQUALS &quot;t2&quot; ) then 
    
    do something
    
    done.

And in my failed attempt, I came up with:


    if (($varA == 1)) &amp;&amp; ( (($varB == &quot;t1&quot;)) || (($varC == &quot;t2&quot;)) ); 
      then
        scale=0.05
      fi

Simple logical operators in Bash

I have a bash script checking the number of CPUs on the platform to efficiently use `-j` option for make, repo, etc.  I use this:

    JOBS=$(cat /proc/cpuinfo | grep processor | tail -1 | sed &quot;s,^.*:.*$[0-9].*$$,\1,&quot;)
    echo -e &quot;4\n$JOBS&quot; | sort -r | tail -1

It works fine. But, I am wondering if there was any built-in function which does the same thing (i.e. calculating the minimum, or maximum)?

how to calculate the minimum of two variables simply in bash?

According to the [R language definition](https://cran.r-project.org/doc/manuals/r-release/R-lang.html#Operators), the difference between `&amp;` and `&amp;&amp;` (correspondingly `|` and `||`) is that the former is vectorized while the latter is not.

According to [the help text](https://stat.ethz.ch/R-manual/R-devel/library/base/html/Logic.html), I read the difference akin to the difference between an &quot;And&quot; and &quot;AndAlso&quot; (correspondingly &quot;Or&quot; and &quot;OrElse&quot;)...
Meaning:
That not all evaluations if they don&#39;t have to be (i.e. A or B or C is always true if A is true, so stop evaluating if A is true)

Could someone shed light here?
Also, is there an AndAlso and OrElse in R?

Boolean operators &amp;&amp; and ||

The logical expression `( a &amp;&amp; b )` *(both `a` and `b` have boolean values)* can be written like `!(!a || !b)`, for example. Doesn&#39;t this mean that `&amp;&amp;` is &quot;unneccesary&quot;? Does this mean that *all* logical expressions can be made only using `||` and `!`? 

Are || and ! operators sufficient to make every possible logical expression?

Why do these logical operators return an object and not a boolean?

    var _ = (obj.fn &amp;&amp; obj.fn() ) || obj._ || ( obj._ = {} );

    var _ = obj &amp;&amp; obj._;

I want to understand why it returns result of `obj.fn()` (if it is defined) OR `obj._` but not boolean result.


Why don&#39;t logical operators (&amp;&amp; and ||) always return a boolean result?

How would you implement logical operators in DOS Batch files?

Logical operators (&quot;and&quot;, &quot;or&quot;) in DOS batch

Why is there no logical xor in JavaScript?

Are the two statements below equivalent?

    SELECT [...]
    FROM [...]
    WHERE some_col in (1,2,3,4,5) AND some_other_expr

and

    SELECT [...]
    FROM [...]
    WHERE some_col in (1,2,3) or some_col in (4,5) AND some_other_expr

Is there some sort of truth table I could use to verify this?

SQL Logic Operator Precedence: And and Or

How do you get the [logical xor][1] of two variables in Python?

For example, I have two variables that I expect to be strings. I want to test that only one of them contains a True value (is not None or the empty string):

    str1 = raw_input(&quot;Enter string one:&quot;)
    str2 = raw_input(&quot;Enter string two:&quot;)
    if logical_xor(str1, str2):
        print &quot;ok&quot;
    else:
        print &quot;bad&quot;

The `^` operator seems to be bitwise, and not defined on all objects:

    &gt;&gt;&gt; 1 ^ 1
    0
    &gt;&gt;&gt; 2 ^ 1
    3
    &gt;&gt;&gt; &quot;abc&quot; ^ &quot;&quot;
    Traceback (most recent call last):
      File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;
    TypeError: unsupported operand type(s) for ^: &#39;str&#39; and &#39;str&#39;

  [1]: http://en.wikipedia.org/wiki/Exclusive_or

How do you get the logical xor of two variables in Python?

Does the ANSI standard *mandate* the logical operators to be short-circuited, in either C or C++?

I&#39;m confused for I recall the K&amp;R book saying your code shouldn&#39;t depend on these operations being short circuited, for they may not. Could someone please point out where in the standard it&#39;s said logic ops are always short-circuited? I&#39;m mostly interested on C++, an answer also for C would be great.

I also remember reading (can&#39;t remember where) that evaluation order isn&#39;t strictly defined, so your code shouldn&#39;t depend or assume functions within an expression would be executed in a specific order: by the end of a statement all referenced functions will have been called, but the compiler has freedom in selecting the most efficient order.

Does the standard indicate the evaluation order of this expression?

    if( functionA() &amp;&amp; functionB() &amp;&amp; functionC() ) cout&lt;&lt;&quot;Hello world&quot;;

Is short-circuiting logical operators mandated? And evaluation order?

I personally like the _exclusive or_, `^`, operator when it makes sense in the context of boolean checks because of its conciseness.  I much prefer to write

    
    if (boolean1 ^ boolean2)
    {
      //do it
    }

than

    if((boolean1 &amp;&amp; !boolean2) || (boolean2 &amp;&amp; !boolean1))
    {
      //do it
    }

but I often get confused looks from other experienced Java developers (not just the newbies), and sometimes comments about how it should only be used for bitwise operations. 

I&#39;m curious as to the best practices regarding the usage of the `^` operator.




Is it good practice to use the xor operator for boolean checks?

The short circuiting behaviour of the operators `&amp;&amp;` and `||` is an amazing tool for programmers.

But why do they lose this behaviour when overloaded? I understand that operators are merely syntactic sugar for functions but the operators for `bool` have this behaviour, why should it be restricted to this single type? Is there any technical reasoning behind this?

Is there actually a reason why overloaded &amp;&amp; and || don&#39;t short circuit?

I know the rules for `&amp;&amp;` and `||` but what are `&amp;` and `|`? Please explain these to me with an example.

Differences in boolean operators: &amp; vs &amp;&amp; and | vs ||

I&#39;m trying to learn python and came across some code that is nice and short but doesn&#39;t totally make sense

the context was:

    def fn(*args):
        return len(args) and max(args)-min(args)

I get what it&#39;s doing, but why does python do this - ie return the value rather than True/False?

    10 and 7-2

returns 5. Similarly, changing the and to or will result in a change in functionality. So

    10 or 7 - 2

Would return 10.

Is this legit/reliable style, or are there any gotchas on this?


How do &quot;and&quot; and &quot;or&quot; act with non-boolean values?

I remember reading a while back in regards to logical operators that in the case of `OR`, using `||` was better than `or` (or vice versa).

I just had to use this in my project when it came back to me, but I can&#39;t remember which operator was recommended or if it was even true.

Which is better and why?




Logical Operators, || or OR?

Which set is short-circuiting, and what exactly does it mean that the complex conditional expression is short-circuiting?
    
    public static void main(String[] args) {
      int x, y, z;
      
      x = 10;
      y = 20;
      z = 30;
      
      // T T
      // T F
      // F T
      // F F
      
      //SET A
      boolean a = (x &lt; z) &amp;&amp; (x == x);
      boolean b = (x &lt; z) &amp;&amp; (x == z);
      boolean c = (x == z) &amp;&amp; (x &lt; z);
      boolean d = (x == z) &amp;&amp; (x &gt; z);
      //SET B    
      boolean aa = (x &lt; z) &amp; (x == x);
      boolean bb = (x &lt; z) &amp; (x == z);
      boolean cc = (x == z) &amp; (x &lt; z);
      boolean dd = (x == z) &amp; (x &gt; z);

    }

Java logical operator short-circuiting

[This](http://www.cppreference.com/wiki/operator_precedence#Notes) is the only place I&#39;ve ever seen `and`, `or` and `not` listed as actual operators in C++. When I wrote up a test program in NetBeans, I got the red underlining as if there was a syntax error and figured the website was wrong, but it is NetBeans which is wrong because it compiled and ran as expected.

I can see `!` being favored over `not` but the readability of `and` &amp;&amp; `or` seems greater than their grammatical brothers. Why do these versions of the logical operators exist and why does seemingly no one use it? Is this truly valid C++ or some sort of compatibility with C that was included with the language?

The written versions of the logical operators

What&#39;s the difference between `&amp;` and `&amp;&amp;` in JavaScript?

Example code:

    var first  = 123;
    var second = false;
    var third  = 456;
    var fourth = &quot;abc&quot;;
    var fifth  = true;
    alert(first &amp; second); // 0
    alert(first &amp; third);  // 72
    alert(first &amp; fourth); // 0
    alert(first &amp; fifth);  // 1

    alert(first &amp;&amp; second); // false
    alert(first &amp;&amp; third);  // 456
    alert(first &amp;&amp; fourth); // abc
    alert(first &amp;&amp; fifth);  // true

It seems like `&amp;&amp;` is a logical `and` which gives me always the second value if both are `true`.

But what is `&amp;`?

(By the way, `&amp;&amp;` seems to be `and` in Python; `&amp;` seems to be `&amp;` in Python)

What&#39;s the difference between &amp; and &amp;&amp; in JavaScript?

What is the difference between the `&amp;` and `&amp;&amp;` logical operators in MATLAB?

What&#39;s the difference between &amp; and &amp;&amp; in MATLAB?

I would like the element-wise logical OR operator. I know &quot;or&quot; itself is not what I am looking for.

I am aware that AND corresponds to `&amp;` and NOT, `~`. But what about OR? 

  [1]: https://stackoverflow.com/questions/21415661/logic-operator-for-boolean-indexing-in-pandas &quot;here&quot;
  [2]: https://stackoverflow.com/questions/15998188/how-can-i-obtain-the-element-wise-logical-not-of-a-pandas-series

Element-wise logical OR in Pandas

Is there no XOR operator for booleans in golang?

I was trying to do something like `b1^b2` but it said it wasn&#39;t defined for booleans.

Is there no XOR operator for booleans in golang?

I read the C# Language Specification on the _Conditional logical operators_ `||` and `&amp;&amp;`, also known as the short-circuiting logical operators. To me it seemed unclear if these existed for nullable booleans, i.e. the operand type `Nullable&lt;bool&gt;` (also written `bool?`), so I tried it with non-dynamic typing:

    bool a = true;
    bool? b = null;
    bool? xxxx = b || a;  // compile-time error, || can&#39;t be applied to these types

That seemed to settle the question (I could not understand the specification clearly, but assuming the implementation of the Visual C# compiler was correct, now I knew).

However, I wanted to try with `dynamic` binding as well. So I tried this instead:

    static class Program
    {
      static dynamic A
      {
        get
        {
          Console.WriteLine(&quot;&#39;A&#39; evaluated&quot;);
          return true;
        }
      }
      static dynamic B
      {
        get
        {
          Console.WriteLine(&quot;&#39;B&#39; evaluated&quot;);
          return null;
        }
      }
    
      static void Main()
      {
        dynamic x = A | B;
        Console.WriteLine((object)x);
        dynamic y = A &amp; B;
        Console.WriteLine((object)y);

        dynamic xx = A || B;
        Console.WriteLine((object)xx);
        dynamic yy = A &amp;&amp; B;
        Console.WriteLine((object)yy);
      }
    }

The surprising result is that this runs without exception.

Well, `x` and `y` are not surprising, their declarations lead to both properties being retrieved, and the resulting values are as expected, `x` is `true` and `y` is `null`.

But the evaluation for `xx` of `A || B` lead to no binding-time exception, and only the property `A` was read, not `B`. Why does this happen? As you can tell, we could change the `B` getter to return a crazy object, like `&quot;Hello world&quot;`, and `xx` would still evaluate to `true` without binding-problems...

Evaluating `A &amp;&amp; B` (for `yy`) also leads to no binding-time error. And here both properties are retrieved, of course. Why is this allowed by the run-time binder? If the returned object from `B` is changed to a &quot;bad&quot; object (like a `string`), a binding exception does occur.

___Is this correct behavior?___ (How can you infer that from the spec?)

If you try `B` as first operand, both `B || A` and `B &amp;&amp; A` give runtime binder exception (`B | A` and `B &amp; A` work fine as everything is normal with non-short-circuiting operators `|` and `&amp;`).

(Tried with C# compiler of Visual Studio 2013, and runtime version .NET 4.5.2.)

Do short-circuiting operators || and &amp;&amp; exist for nullable booleans? The RuntimeBinder sometimes thinks so

I know that in JavaScript you can do:

    var oneOrTheOther = someOtherVar || &quot;these are not the droids you are looking for...&quot;;

where the variable `oneOrTheOther` will take on the value of the first expression if it is not `null`, `undefined`, or `false`. In which case it gets assigned to the value of the second statement. 

However, what does the variable `oneOrTheOther` get assigned to when we use the logical AND operator? 

    var oneOrTheOther = someOtherVar &amp;&amp; &quot;some string&quot;;

What would happen when `someOtherVar` is non-false?  
What would happen when `someOtherVar` is false?

Just learning JavaScript and I&#39;m curious as to what would happen with assignment in conjunction with the AND operator.

Javascript AND operator within assignment

Assume myObj is null.  Is it safe to write this?  

    if(myObj != null &amp;&amp; myObj.SomeString != null)

I know some languages won&#39;t execute the second expression because the &amp;&amp; evaluates to false before the second part is executed.

Is relying on &amp;&amp; short-circuiting safe in .NET?

Is it possible in Handlebars to check if a string is equal to another value without registering a helper? I can&#39;t seem to find anything relevant to this in the Handlebars reference.

For example:

    {{#if sampleString == &quot;This is a string&quot;}}
    ...do something
    {{/if}}

Handlebarsjs check if a string is equal to a value

Is there such a thing? It is the first time I encountered a practical need for it, but I don&#39;t see one listed [in Stroustrup][1]. I intend to write:

    // Detect when exactly one of A,B is equal to five.
    return (A==5) ^^ (B==5);

But there is no `^^` operator. Can I use the bitwise `^` here and get the right answer (regardless of machine representation of true and false)? I never mix `&amp;` and `&amp;&amp;`, or `|` and `||`, so I hesitate to do that with `^` and `^^`. 

I&#39;d be more comfortable writing my own `bool XOR(bool,bool)` function instead.

  [1]: https://en.wikipedia.org/wiki/The_C%2B%2B_Programming_Language


Logical XOR operator in C++?

I am getting back into web development, and have been trying to go over the nuances of jscript recently. I was pouring through the source of the THREEx extension library built on top of Three.JS and noticed this function

    THREEx.KeyboardState.prototype.pressed	= function(keyDesc)
    {
	    var keys	= keyDesc.split(&quot;+&quot;);
	    for(var i = 0; i &lt; keys.length; i++){
		    var key		= keys[i];
		    var pressed;
		    if( THREEx.KeyboardState.MODIFIERS.indexOf( key ) !== -1 ){
			    pressed	= this.modifiers[key];
		    }else if( Object.keys(THREEx.KeyboardState.ALIAS).indexOf( key ) != -1 ){
			    pressed	= this.keyCodes[ THREEx.KeyboardState.ALIAS[key] ];
		    }else {
			    pressed	= this.keyCodes[key.toUpperCase().charCodeAt(0)];
		    }
		    if( !pressed)	return false;
	    };
	    return true;
    }

I am looking in particular at the line here:

    if( THREEx.KeyboardState.MODIFIERS.indexOf( key ) !== -1 ){

I am not familiar with this !== operator. I checked w3schools and their logical operators list does not have this one included. I am not sure if this is misspelled and the browsers simply count it as != or if it has some other meaning. Also I was wondering whether this is actually a single logical operator or whether it is some kind of combination, like ! + ==?


Javascript logical &quot;!==&quot; operator?

&gt; **Possible Duplicate:**  
&gt; [What is the diffference between the | and || or operators?](https://stackoverflow.com/questions/35301/what-is-the-diffference-between-the-and-or-operators)  

&lt;!-- End of automatically inserted text --&gt;

Logical AND and OR:

    (x &amp; y)
    (x | y)

Conditional AND and OR:

    (x &amp;&amp; y)
    (x || y)

I&#39;ve only known about conditional operands up to this point. I know what it does and how to apply it in if-statements. But what is the purpose of logical operands?

All Logical Operators Solutions on Gang of Coders

Total of 29 Logical Operators Solutions

Is there any reason for using if(1 || !Foo())?

Simple logical operators in Bash

how to calculate the minimum of two variables simply in bash?

Boolean operators && and ||

Are || and ! operators sufficient to make every possible logical expression?

Why don't logical operators (&& and ||) always return a boolean result?

Logical operators ("and", "or") in DOS batch

Why is there no logical xor in JavaScript?

SQL Logic Operator Precedence: And and Or

How do you get the logical xor of two variables in Python?

Is short-circuiting logical operators mandated? And evaluation order?

Is it good practice to use the xor operator for boolean checks?

Is there actually a reason why overloaded && and || don't short circuit?

Differences in boolean operators: & vs && and | vs ||

How do "and" and "or" act with non-boolean values?

Logical Operators, || or OR?

Java logical operator short-circuiting

The written versions of the logical operators

What's the difference between & and && in JavaScript?

What's the difference between & and && in MATLAB?

Element-wise logical OR in Pandas

Is there no XOR operator for booleans in golang?

Do short-circuiting operators || and && exist for nullable booleans? The RuntimeBinder sometimes thinks so

Javascript AND operator within assignment

Is relying on && short-circuiting safe in .NET?

Handlebarsjs check if a string is equal to a value

Logical XOR operator in C++?

Javascript logical "!==" operator?

What is the difference between logical and conditional AND, OR in C#?