# PHP: Commutative operation

Do you remember the basic rule of arithmetic that changing the order of the numbers we're adding doesn't change the sum? It's one of the most basic and intuitive rules of arithmetics, it's called the commutative law.

A binary operation is considered commutative if you get the same result after swapping operands. Obviously, addition is a commutative operation: 3 + 2 = 2 + 3.

But is subtraction a commutative operation? Of course not: 2 - 3 ≠ 3 - 2. In programming, this law applies in the same way as in arithmetic.

Moreover, most of the operations we face in real life aren't commutative. In conclusion, you should always pay attention to the order of things you're working with.

## Instructions

Write a program that counts and sequentially displays the values of the following mathematical expressions: "3 to the power of 5" and "-8 divided by -4".

Note that the results will appear stuck together, on one line, and without any spaces. We'll learn how to deal with this problem in future lessons.

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

• 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.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.

## Definitions

• Commutativity is the property of an operation wherein changing the order of operands doesn't affect the result. For example, addition is a commutative operation; changing the order of the numbers we're adding doesn't change the result.

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