Before we move on, let's take a look at the basic terminology. An operation sign, such as
+, is called an operator. Operators perform operations on certain values, which are called operands. The operators themselves are usually represented by one or more characters,, and occasionally by a word. Most of the operators are identical to those you'll have seen in math class.
<?php print_r(8 + 2);
In this example
+ is an operator, and the numbers
2 are operands.
When it comes to addition, we have two operands: one to the left of the
+ sign and one to the right. Operations with two operands are called binary operations. If at least one operand is omitted, e.g.,
3 + ;, the program will end with a syntax error.
Operations can be more than just binary, they can also be unary (one operand), and even ternary (three operands). Moreover, operators may look the same but denote different operations. The symbols
- are used as more than just operators. When it comes to negative numbers, the minus sign becomes part of the number:
<?php print_r(-3); // => -3
Above is an example of applying a unary operation to the number
3. The minus operator before the three tells the interpreter to take the number
3 and find the opposite, which is
This can be a bit confusing because
-3 is both a number in itself and an operator with an operand, but this is just how programming languages are structured.
<?php // Same as 4 - 3 print_r(4 + -3); // => 1
The same goes for the plus sign:
<?php print_r(+3); // => 3 print_r(1 + +3); // => 4
Write a program that calculates the difference between the numbers
-81 and displays the answer 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.
Arithmetic operations include addition, subtraction, multiplication and division.
A unary operation is an operation with one operand. For example,
-3is a unary operation to get the opposite of three.
A binary operation is an operation with two operands. For example,
3 + 9.