PHP: Ternary operator

Look at the definition of this function, which returns the modulus of a given number:

<?php

function abs($number)
{
    if ($number >= 0) {
        return $number;
    }

    return -$number;
}

abs(10);  // 10
abs(-10); // 10

Can we write it more concisely? Something like return return ОТВЕТ В ЗАВИСИМОСТИ ОТ УСЛОВИЯ? That would require an expression following return, but if is a statement, not an expression.

In PHP, there's a construct that works like theif-else construct, but is an expression. It's called the ternary operator.

The ternary operator is the only JavaScript operator that takes three operands:

<?php

function abs($number)
{
    return $number >= 0 ? $number : -$number;
}

It generally looks like this:

<predicate> ? <expression on true> : <expression on false>

Let's rewrite the initial version of getTypeOfSentence() in the same way:

Before:

<?php

function getTypeOfSentence($sentence)
{
    $lastChar = substr($sentence, -1);

    if ($lastChar === '?') {
        return 'question';
    }

    return 'normal';
}

After:

<?php

function getTypeOfSentence($sentence)
{
    $lastChar = substr($sentence, -1);

    return ($lastChar === '?') ? 'question' : 'normal';
}

getTypeOfSentence('Hodor');  // normal
getTypeOfSentence('Hodor?'); // question

---

If you remember the main strength of expressions, then you probably figured out by now that you can nest a ternary operator in another ternary operator. ** Don't do it :)** This sort of code is hard both to read and to debug, it's very bad practice.

Instructions

Implement the flipFlop() function, which takes a string as input and, if that string is 'flip', it returns the string 'flop'. Otherwise, the function needs to return 'flip'.

Call examples:

<?php

flipFlop('flip'); // 'flop'
flipFlop('flop'); // 'flip'

Try writing two versions of the function: one with the usual if-else, and one with a ternary operator.