php "if" condition mystery

I am running into a funny problem with a mischievous "if" condition :

$condition1="53==56";
$condition2="53==57";
$condition3="53==58";
$condition=$condition1."||".$condition2."||".$condition3;
if($condition)
{
    echo "blah";
}
else
{
    echo "foo";
}

Why doe开发者_如何学运维s the if condition pass? Why does php echo "blah"? What do I do to make php evaluate the "if" statement and print "foo"?

The problem here is that you're putting your expressions in strings!

Your $condition1, $condition2, and $condition3 variables contain strings, and not the result of an expression, and the same goes for your $condition variable which will be a string that looks like 53==56||53==57||53==58. When PHP evaluates a string it considers it true if it is not empty and not equal to 0, so your script will output blah.

To fix this you just need to take your expressions out of the strings. It should look like this:

$condition1 = 53 == 56; // false
$condition2 = 53 == 57; // false
$condition3 = 53 == 58; // false
$condition = $condition1 || $condition2 || $condition3; // false || false || false = false

if ($condition) {
    echo 'blah';
} else {
    echo 'foo'; // This will be output
}

You're evaluating strings as booleans; they'll aways be true (except the strings "" and "0". Get rid of almost all of the quotes in your program.

Those aren't conditions, they're strings.

$condition1=53==56;
$condition2=53==57;
$condition3=53==58;
$condition=$condition1 || $condition2 || $condition3;
if($condition)
{
    echo "blah";
}
else
{
    echo "foo";
}

Because you're not checking those variables, it's saying if (String) will always return true. (unless "")

You should be doing:

if(53==56 || 53==57 || 53==58)
{
    echo "blah";
}
else
{
    echo "foo";
}

All $condition* variables will evaluate to true. This is how PHP sees it:

if("53==56" || "53==57" || "53==58")

What you want is this:

$condition1 = 53==56;
$condition2 = 53==57;
$condition3 = 53==58;

It's because you're evaluating a string, and strings other than empty strings evaluate to true.

You are concatting a string together, a non-empty string equals TRUE in php.

Because when the if passes, $condition is a string (a concatenation of) containing the text of your conditions. Try using if(eval($condition)).

String always evaluate to true if its not empty
And btw php make implicit conversion to boolean