CODEWITHSUNDEEP
javascript
phlipinmi
phlipinmi

Reputation: 63

What is the difference between these comparisons using || and ,

What is the difference between these two statements. I get different results when I use these interchangeably. I was hoping that someone could explain this for me. So whats the difference between, this...

else if ( ( elecshow ==2,3,4,5,6,8,9,10,16 ) )

and this...

else if ( ( elecshow ==2 ) || ( elecshow ==3 ) || ( elecshow ==4 ) || ( elecshow ==5 ) || ( elecshow ==6 ) || ( elecshow ==8 ) || ( elecshow ==9 ) || ( elecshow ==10 ) || ( elecshow ==16 ) )

I know this is simple stuff but your input would be appreciated.

Upvotes: 0

Views: 51

Answers (2)

Bergi
Bergi

Reputation: 664406

Check what the comma operator actually does. Your first snippet is equivalent to

else if ( ((((((((elecshow ==2),3),4),5),6),8),9),10),16 )

or (if we assume that evaluating elecshow doesn't throw etc.) just

else if ( 16 )

You will need to use the second one, although you might be able to shorten it to something like

else if (elecshow > 1 && elecshow <= 10 && elecshow != 7 || elecshow == 16)

Upvotes: 2

dee-see
dee-see

Reputation: 24078

The comma operator

evaluates each of its operands (from left to right) and returns the value of the last operand

Combined with the fact that == has higher precedence than , what happens here is that elecshow ==2 is evaluated, then 3, then 4, ... and finally 16.

The last evaluation is returned and, 16 being a truthy value, the execution will enter the else if.

The result differs from

else if ( ( elecshow ==2 ) || ( elecshow ==3 ) || ( elecshow ==4 ) || ( elecshow ==5 ) || ( elecshow ==6 ) || ( elecshow ==8 ) || ( elecshow ==9 ) || ( elecshow ==10 ) || ( elecshow ==16 ) )

simply because it's an entirely different operator!

Upvotes: 2

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