Functions in any programming language have fundamental properties. These properties help you understand how a function will behave in different situations, how to test it, and where to use it. One of these properties is determinism.

A deterministic function always returns the same result for the same input data. For example, a function that counts the number of characters can be called deterministic:

<?php

strlen('hexlet'); // 6
strlen('hexlet'); // 6

strlen('wow'); // 3
strlen('wow'); // 3

The strlen() function can be called endlessly with the same argument, and it will always return the same result.

Non-deterministic functions

The opposite type is non-deterministic functions. They can return different results for the same input data or in the absence of it (functions without parameters). A good example is the rand() function, which returns a random number:

<?php

rand(); // 827606195
rand(); // 635369726

This function has no arguments, but its result is different every time. If even one call out of millions gives a different result, the function is considered non-deterministic.

Deterministic:              Non-deterministic:
strlen('abc') → always 3    rand() → 827606195
strlen('abc') → always 3    rand() → 635369726
strlen('abc') → always 3    rand() → 142503087

Why this matters

Determinism affects how we work with functions.

• deterministic functions are easy to test and predict;
• they are easier to optimize and reuse;
• non-deterministic functions are harder to check, because the result changes.

That's why, wherever possible, it's better to aim for a function to be deterministic.

In a board game, you roll a die and get a number from 0 to 10. Write a program that simulates this roll: it prints a random integer in the range from 0 to 10 to the screen. For this task you'll need the rand() function, which can take two numbers: the start and the end value of the range.

Try to solve this task in a single line.