PHP: Priority of operations
Look closely at the expression 2 + 2 * 2 and try and work out the answer.
The correct answer is 6.
If you got 8, then this lesson is for you. You'll have studied the order of operations in high school math. This concept defines the order in which operations are to be performed. For example, multiplication and division have a higher precedence than addition and subtraction, and exponentiation comes before all other arithmetic operations, e.g., 2 ** 3 * 2 gives us 16.
But sometimes, we have to perform calculations in a non-standard order. In complex cases, precedence can (and must) be set with parentheses, just like we did in high school, e.g, (2 + 2) * 2.
Parentheses fit with any operation. They can be nested into each other as many times as you need. Here are a couple of examples:
<?php
print_r(3 ** (4 - 2)); // => 9
print_r(7 * 3 + (4 / 2) - (8 + (2 - 1))); // => 14
The main thing is to make sure to close the parentheses in the correct order. This often causes errors not just for beginners but also for experienced programmers. For convenience's sake, do the opening and closing parentheses first, and then write the inside part. The editor on our site (and most other code editors) does this automatically: you write (, and the editor immediately adds ). This also applies to other paired characters, such as quotation marks. We'll talk about them in future lessons.
Sometimes, an expression can be visually cumbersome. In such cases, parentheses can come in handy without affecting the order of operations. For example, the task from the previous lesson gets clearer if you have parentheses.
Before:
<?php
print_r(8 / 2 + 5 - -3 / 2); // => 10.5
After:
<?php
print_r(((8 / 2) + 5) - (-3 / 2)); // => 10.5
Note: code is written for humans, since they'll be the ones to read it, the machine just executes it. For the machine, code is either valid or invalid, it doesn't recognize "more" or "less" valid code. Explicit prioritization makes it easier for other developers to read your code.
Instructions
Here's a calculation: 70 * 3 + 4 / 8 + 2.
Place parentheses so that both additions, (3 + 4) and (8 + 2) will be calculated first. Print the result on the screen.
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.
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.
Your exercise will be checked with these tests:
1<?php // phpcs:ignore PSR1.Files.SideEffects
2
3namespace HexletBasics\Arithmetics\Priority;
4
5use PHPUnit\Framework\TestCase;
6
7\HexletBasics\Functions\runScript();
8
9class Test extends TestCase
10{
11 public function test()
12 {
13 $expected = '49';
14 $this->expectOutputString($expected);
15 require 'index.php';
16 }
17}
18Teacher's solution will be available in:
