I came across this question. What am I missing?
function ninja($x, $y, $z)
{
if ($y != $z && $x == $y && $x == $z) {
return "Yes";
}
return "No";
}
For what values of $x, $y, $z will this function return "Yes" ?
-
Here's a good link about "tautologies" (the logical expression is always 'true') and "contradictions" (always 'false'): people.hofstra.edu/stefan_waner/realworld/logic/logic2.htmlpaulsm4– paulsm42014-03-15 05:52:16 +00:00Commented Mar 15, 2014 at 5:52
Add a comment
|
4 Answers
Since == and != allow type juggling, various combinations of values will allow the function to return Yes. One version is
function ninja($x, $y, $z) {
if ($y != $z && $x == $y && $x == $z) {
return "Yes";
}
return "No";
}
echo ninja(0, 'a', 'b');
Since non numeric strings - when compared to and type juggled to an integer - have the value 0, the strange result is;
* $x == $y (0 == 'a')
* $x == $z (0 == 'b')
* $y != $z ('a' != 'b') (both are strings, so no type juggling)
The documentation of comparison operators will give some more type juggling ideas, the short version is that there are probably more combinations, but they're not always obvious. Reading it gives good motivation to learn to use === and !== though :)
Comments
According to Your logic:-
if ($y != $z && $x == $y && $x == $z)
so here
1. $y != $z
2. $x == $y
3. $x == $z
if I consider point 2 and 3 then
i. $x == $y
ii. $x == $z this means $y == $z
But You have a condition $y != $z
So Your above if() condition will never be true. It always return false.
1 Comment
Hans
Mathematically, but not in PHP. ii. is not correct for PHP.
This will return true.
ninja(0, false, 'a');
One of the quirks of PHP.
Comments
if you take
$x=0;
$y='z'; #only alphabet character
$z='x'; #only alphabet character
Because PHP is [loosely-typed] language you can always cast string to number by adding a zero to it. So you have to take $x value is always 0.
