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PHP: Constants

Some data, such as mathematical constants, never change. Take the number π. It's always approximately 3.14 and cannot change.

It's generally accepted in PHP to use constants to refer to this kind of data.


  const PI = 3.14;
  print_r(PI); // => 3.14

Creating a constant is different from creating a variable. It starts with the keyword const followed by the constant name. We don't need the dollar sign. Then we assign it the desired value. Constants are usually named with uppercase letters, with _ as a separator. A constant, like a variable, can be used in any expression. The only limitation is that the constant can't be changed, which sounds pretty logical.

PHP has a lot of built-in constants that can be used anywhere in the program. Some of them are:

  • PHP_VERSION — the current version of PHP
  • PHP_MAXPATHLEN — maximum file name length
  • PHP_INT_MAX — the maximum possible value of integers


Create a constant, DRAGONS_BORN_COUNT and write the number 3 in it. This is the number of dragons born to Daenerys.

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 🙄

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  • A constant is a way of storing information and naming it for later use in code; constants cannot be changed, unlike variables.

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