RE: [PHP] Re: question about ? :

> -----Original Message----- > From: Lee Doolan [mailto:lee@affero.com] > Sent: 19 June 2002 17:08 > To: php-general@lists.php.net > Subject: [PHP] Re: question about ? : > > > >>>>> "Mike" == Mike Ford <M.Ford@lmu.ac.uk> writes: > > >> -----Original Message----- From: Joel Boonstra > >> [mailto:jboonstra@gospelcom.net] Sent: 19 June 2002 14:00 > >> > >> > OK, try this: why does > >> > > >> > $x = 3 + 5 - 7; > >> > > >> > produce different results from > >> > > >> > $x = 3 + (5 - 7); > > I still dont understand why something like > > <expr-a> ? <expr-b> : <expr-c> > > should evaluate differently than > > <expr-a> ? <expr-b> : (<expr-c>) > > where <expr-c> is ternary. consult the original > question for an example. OK, we need to expand that slightly to get a double-ternary into the mix, if you see what I mean: a ? x : c ? y : z Now, ?: is a left-associative operator in PHP, so this is equivalent to: (a ? x : c) ? y : z or, in other words: if a is true then use the Boolean value of x, else use the Boolean value of c, to decide whether to return y or z. Your other alternative is: a ? x : (c ? y : z) which is quite different (if a is true return x, otherwise use the Boolean value of c to decide whether to return y or z)! OK? Cheers! Mike --------------------------------------------------------------------- Mike Ford, Electronic Information Services Adviser, Learning Support Services, Learning & Information Services, JG125, James Graham Building, Leeds Metropolitan University, Beckett Park, LEEDS, LS6 3QS, United Kingdom Email: m.ford@lmu.ac.uk Tel: +44 113 283 2600 extn 4730 Fax: +44 113 283 3211