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PHP: Weak typing

We know about two different data types: integers and strings. We could add integers to each other, because addition is an operation for the type "integer".

What if we apply this operation to an integer and a string, instead of two integers?

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

Despite of '7' being a string rather than integer, the PHP interpreter printed '8' as result, as if we were adding two integers. When PHP encounters conflicting types, it tries to convert information on its own. In the above example it converted string '7' into integer 7 and then easily added 1 to 7.

Not all languages support this. PHP is a weakly typed language. It knows about different types (integers, strings etc.), but it doesn't enforce them, trying to convert data when it seems reasonable.

In a strongly typed language it's not possible to add a string to a number.

PHP was created to cater to the Internet environment, and all information on the Internet is strings. Even when you input your phone number or birth date on some website, this information arrives to server as strings rather than numbers. This is why the creators of the language decided that the automatic type conversion would come in handy.

Such automatic non-explicit type conversion is indeed handy. When put into practice, however, it can create tons of errors and problems that are difficult to locate. The code can be workable or not workable sometimes, depending on"luck" in each case. It will take time for a programmer to notice that.

In the future exercises you will encounter such behavior. Very often you will ask yourself "why is my code not working the way I'm expecting?".

Weak typing is a very important aspect in PHP development.


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

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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