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PHP: Weak typing

We know two different data types: numbers and strings. We could, for example, add numbers, because the addition operation is an operation for the "number" type.

But what if you add a number to a string?

print_r(1 + '7'); // => 8

Although though '7' is a string and not a number, the PHP interpreter gave the answer 8, as if we were adding two numbers. When PHP sees a type mismatch, it tries to convert the information itself. In this case, it converted the string '7' to the number 7, and then happily added 1 and 7.

Not all languages can do this. PHP is a language with weak typing. It recognizes different data types (numbers, strings, etc.), but doesn't use them too strictly, trying to convert data when it seems reasonable.

In strongly typed languages, adding a number to a string won't work.

PHP was created for the internet, and on the internet, all information is strings. Even when you type a phone number or a birth year on a website, that information goes to the server as a string, not as a number. So the designers of the language decided that automatic type conversion was the best option.

This tacit automatic type conversion is indeed convenient. But in practice, this feature causes a lot of errors, which are difficult to find. The code may work or fail, depending on whether you're lucky enough for the automatic conversion to have been done correctly A programmer may not notice this immediately.

You'll encounter these cases more than once in future tasks. You'll often ask, "Why doesn't my code work the way I expect?".

Weak typing is a red thread running through all PHP development.


Print the result of the expression: 7 - (-8 - -2). Try making 7 a string instead of a number. Experiment with other numbers too.

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

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