Why does PHP consider 0 to be equal to a string?

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I have the following piece of code:

$item['price'] = 0;
/* Code to get item information goes in here */
if($item['price'] == 'e') {
    $item['price'] = -1;
}

It is intended to initialize the item price to 0 and then get information about it. If the price is informed as 'e' it means an exchange instead of a sell, which is stored in a database as a negative number.

There is also the possibility to leave the price as 0, either because the item is a bonus or because the price will be set in a later moment.

But, whenever the price is not set, which leaves it with the initial value of 0, the if loop indicated above evaluates as true and the price is set to -1. That is, it considers 0 as equal to 'e'.

How can this be explained?

When the price is provided as 0 (after initialization), the behavior is erratic: sometimes the if evaluates as true, sometimes it evaluates as false.*

evaluate numbers php string
9 Answers

Basically, always use the === operator, to guarantee type safety.

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Admin1

I think it is best to show by examples I did, while running into the same weird behavior. See my test case and hopefully it will help you understand the behavior better:

// Normal comparison using the == Operator
echo (0 == "0"); // true
echo (0 == "a"); // true
echo (0 == "safta!"); // true
echo (1000 == "bla"); // false. It appears that PHP has a weird behavior only with the number / string 0 / "0" according to the past 3 examples.
echo (23 == "23"); // true. So as we said, PHP has a problem (not a problem but weird behavior) only when the number / string 0 (or "0") is present
echo (23 == "24"); // false. values aren't equal (unlike last example). The type is less relevant with the == operator as we can see.

// Now using the === and !== Operators
echo ("0" === 0); // false, since === requires both value and type to be the same. Here, type is different (int vs string)
echo ("0" !== 0); // true because they aren't the same in terms of === comparison (type is different and that's why it's true)
echo ("bla" === "blaa"); // false because the values are not the same. The type is the same, but === checks for both equal type and equal value.

//Now using casting and === Operator:
echo ((string)123 === "123"); // true. The casting of the int 123 to string changed it to "123" and now both variables have same value and are of same type
echo ((int)"123" === 123); // true. The casting of the string 123 to int, changed it to int, and now both variables are of same value and type (which is exactly what the === operator is looking for)

// Now using casting and == Operator. Basically, as we've seen above, the == care less for the
// type of var, but more to the value. So the casting is less relevant here, because even
// without casting, like we saw earlier, we can still compare string to int with the == operator
// and if their value is same, we'll get true. Either way, we will show that:
echo ((string)123 == "123"); // true. The casting of the int 123 to string changed it to "123" and now both vars have same value and are of same type
echo ((int)"123" == 123); // true. The casting of the string 123 to int, changed it to int, and now both vars are of same value and type (which is exactly what the === operator is looking for)
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