PHP: Elvis operator

Imagine the following problem: users can have names and pseudonyms on a given website. The name isn't necessary, but a user has one, this person should be addressed by their first name, and if not, you should address them by their pseudonym.

Let's try to assemble a string that greets users according to these requirements:

<?php

function generateGreeting($name, $nickname)
{
    if ($name) {
        return "Hello, {$name}!";
    } else {
        return "Hello, {$nickname}!";
    }
}

generateGreeting('Bob', 'CoolBob86'); // 'Hello, Bob!'
generateGreeting('', 'CoolBob86');    // 'Hello, CoolBob86!'

We've taken advantage of the fact that PHP converts types. In the if ($name) code, PHP will turn $name into a bool type; if it's an empty string, it will return false, otherwise, it'll return true.

You can use a ternary operator to write it in an even shorter way:

<?php

function generateGreeting($name, $nickname)
{
    return $name ? "Hello, {$name}!" : "Hello, {$nickname}!";
}

This is a common situation: we work with bool values and get the first value if it's true and the second if it isn't.

In PHP, there's a special operator for such cases:

<?php

function generateGreeting($name, $nickname)
{
    $user = $name ?: $nickname;
    return "Hello, {$user}!";
}

?: is a binary operator that returns the first operand if it's true, and the second if it isn't.

It's called Elvis because:

Also, Elvis sounds a bit like "else if".

Instructions

Write a function, generateAmount(), that takes two numbers: the number of items and the cost of an audit. If there are 0 goods, the function returns the cost of the audit multiplied by 3. If there aren't 0 goods, the function returns the number of goods.

Call examples:

<?php

generateAmount(0, 2);   // 6
generateAmount(0, 5);   // 15
generateAmount(1, 2);   // 1
generateAmount(12, 49); // 12