php - How to Convert Boolean to String

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I have a boolean variable which I want
to convert to a string

$res =
            true;

I need it the
converted value to also be in the format "true" "false" not
"0"
"1"

$converted_res =
            "true";
$converted_res =
            "false";

I've
tried:

$converted_res =
            string($res);
$converted_res =
            String($res);

but it
tells me string and String are not
recognized functions. How do I convert this boolean to a string in the format "true" or
"false" in php?

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class="normal">Answer

Simplest
solution:

$converted_res = $res ?
'true' : 'false';