problem in boolean expression with if statement

Question

I need some confirmation. I always get correct o/p but someone told me following expression will not work

Thanks in advance.

#define a 11

#define b 12

#define c 13     
    // I want if array[i] has values of any of these  then do something
    if( array[i] ==  (a) ||(b) ||( c))    
   // some function    
  else    
  printf("no match");

Wouldn't the conditional always evaluate to true here? array[i] == (a) become a don't care because (b=12) != 0 which would yield true (same for (c) but the b condition would short-circuit)? It's been awhile since my C days... — Austin Salonen
– Austin Salonen, Commented Jul 21, 2011 at 15:19
@ Everyone... Thanks you all for helping me and clearing my doubts — samprat
– samprat, Commented Jul 21, 2011 at 15:29

rtheunissen · Accepted Answer · 2011-07-21 15:14:08Z

2

 if (array[i] ==  a || array[i] == b || array[i] == c){
       ... 
   }

I do wish sometimes that you could say if (array[i] == [a, b, c]) or something to that effect.

answered Jul 21, 2011 at 15:14

rtheunissen

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Seb Holzapfel · Accepted Answer · 2011-07-21 15:17:20Z

2

What you're doing is or'in the result of the boolean evaluation array[i]==a directly towards b, c.

In other words, ( (array[i] == a) || (b) || (c) ) is effectively what you're doing - probably not what you intended!

You will need to evaluate the boolean expressions separately:

(array[i] == a) || (array[i] == b) ...

answered Jul 21, 2011 at 15:17

Seb Holzapfel

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2 Comments

Austin Salonen Over a year ago

To confirm my comment on the question: Since b != 0, the conditional would always be true -- correct?

Seb Holzapfel Over a year ago

Yep, looks to me like that's the case.

Sam Holloway · Accepted Answer · 2011-07-21 15:14:27Z

1

Replace your code with this:

if( array[i] == a || array[i] == b || array[i] == c)

Each part of the boolean condition must be a complete expression. While what you wrote is valid C code, it doesn't achieve what you want: you need to make an array element comparison in every part.

answered Jul 21, 2011 at 15:14

Sam Holloway

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2 Comments

samprat Over a year ago

Thanks for the explanation. I will try and let you guys know

samprat Over a year ago

--> Thanks for quick and efficient reply.

Carl Norum · Accepted Answer · 2011-07-21 15:15:55Z

0

"Someone" is correct. You need to use:

if ((array[i] == a) || (array[i] == b) || (array[i] == c))

Your program does not always produce correct output. Try it with any i not equal to 11, 12, or 13.

answered Jul 21, 2011 at 15:15

Carl Norum

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