PHP switch($p) take the first case if $p == 1 - php

Question

I have this code:
$r = do_something($data);
if ($r == 1)
{
echo "it is 1";
}
switch ($r)
{
case "a":
print "a";
break;
case "b":
print "b";
break;
default:
print "default";
}
With this code the output should be:
it is 1
default
but the surprise is that the output is:
it is 1
a
How is this possible?
edit: after some test i see that:
$r === true.
so the new question is: when the var is true how work the switch?

Answer 1

PHP's "type juggling" rules are rather tricky, and occasionally unintuitive and even controversial. There's a great big table in the manual showing what happens when you make comparisons of various sorts, but to explain your particular case:
You are working with three different types: $r is currently true, which is a boolean; the if statement tests against 1, which is an integer; and the switch statement tests against "a" and "b", which are strings.
When you compare a boolean to an integer, PHP first converts the integer to a boolean, using the rule that 0 converts to false, and anything else converts to true. This has the effect in your case of $r == 1 evaluating to true, but $r == 42 would also evaluate to true.
When you compare a boolean to a string, a similar thing happens, but here the string gets converted according to this rule: an empty string is false, anything else is true. So $r == "a" also evaluates to true in your example, which is why that branch of the switch statement is executed.
To get the result you were hoping for, you need to force the type conversion to happen in a different way. There are a few ways to do this, but the simplest in your case is to cast $r to the same type as what you're comparing it against:
(int)$r will give you the integer 1 for a value of true, and 0 for false, so if ( (int)$r == 1 ) will give the same result, but be clearer that $r wasn't actually an integer at that point in the code.
more importantly, (string)$r will give you the string "1", so switch( (string)$r ) won't have to do any "type juggling" to compare against strings like "a" and "b", and you won't get any surprises there.

Answer 2

I think your do_something($data) function returns 1 if it does what it suppose to do. I tried this code and it works. Here it is.
function do_something($data){
return 1;
}
$r= do_something('abc');
if ($r == 1)
{
echo "it is 1<br />";
}
switch ($r)
{
case "a" : print "a"; break;
case "b" : print "b"; break;
default : print "default";
}
OUTPUT:
it is 1
default