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PHP: Finding a starting position

One of the more frequent tasks when working with strings is to determine whether one string is a part (substring) of another string. Most programming languages have a built-in function for this very task. In PHP, there's no such function, we imitate it by using mb_strpos(). This function searches for the position of the first occurrence of one string in another.


if (mb_strpos('Валар Моргулис', 'Morgulis')) { // 6
    // ...

In the example above, the function will return 6, which corresponds to the index of the letter M.


if (mb_strpos('Valar Morghulis', 'Valar')) { // 0
    // ...

And in this example, it returns 0, which corresponds to the first letter of the string. There's a mistake often made by beginners in this kind of code. In PHP 0 is treated as false, а значит, условие не выполнится. Правильная проверка выглядит так:


if (mb_strpos('Valar Morghulis', 'Valar') !== false) {
    // ...

The mb_strpos() function returns false if no substring was found, so you can use a strict comparison with false.


Complete the implementation of startsWith(), which determines whether a string starts with a given substring.


startsWith('Hexlet', 'et'); // false
startsWith('Hexlet', 'Hex'); // true
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:

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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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