PHP: Switch construction

Many languages include a switch in addition to the conditional if construct. This is a specialized version of if, designed for certain cases. For example, it makes sense for us to have an if else chain for equality checks. For example:

<?php

if ($status === 'processing') {
    // Doing it once
} elseif ($status === 'paid') {
    // Doing it twice
} elseif ($status === 'new') {
    // Doing it three times
} else {
    // Doing it four times
}

This composite check has one distinguishing feature, each branch here is a check for the value of the status variable. Switch allows you to write this code in a shorter and more expressive way:

<?php

switch ($status) {
    case 'processing': // status == processing
        // Doing it once
        break;
    case 'paid': // status == paid
        // Doing it twice
        break;
    case 'new': // status == new
        // Doing it three times
        break;
    default: // else
        // Doing it four times
}

A switch is a rather complicated construction in terms of the number of elements it consists of:

• An external definition containing the keyword switch. A variable whose values switch use to select a behavior. And curly brackets for behavior branches.
• The case and default constructions, where the behavior for different values of the variable is described. Each case corresponds to an if in the example above. default is a special situation, corresponding to the else branch in conditional constructions. Like with else, there's no need to specify default.
• break is needed to prevent it from not working properly. If it's not specified, then after the desired case is executed, the execution will go to the next case and so on either until it reaches the nearest break, or until the end of the switch.

The curly brackets in the switch don't define a block of code like they did elsewhere. Only the syntax shown above is acceptable. In other words, you can use case or default there. But inside each case (and default) the situation is different. You can execute any code you like here:

<?php

switch ($count) {
    case 1:
        // Doing something useful
        break;
    case 2:
        // Doing something useful
        break;
    default:
        // Doing something
}

Sometimes, the result inside case means ending the function containing the switch. If this happens, you need to return it outside somehow. There are two ways to do this.

The first way. Create a variable before switch, fill it with something in case and then return the value of that variable outward at the end.

<?php

function doSomethingGood($count)
{
    // Filling it
    switch ($count) {
        case 1:
            $result = 'one';
            break;
        case 2:
            $result = 'two';
            break;
        default:
            $result = null;
    }

    // Return
    return $result;
}

The second way is easier and shorter. Instead of creating a variable, case allows you to internally do a normal return from a function. And since no code is executed after return we can get rid of break:

<?php

function doSomethingGood($count)
{
    switch ($count) {
        case 1:
            return 'one';
        case 2:
            return 'two';
        default:
            return null;
    }
}

Though switch is present in the code, you can always find a way to avoid it. The key benefit of using it is that it better expresses the programmer's intention when checking the values of a particular variable. Although there's now physically more code, it's easier to read than loads of elseif blocks.

Instructions

Write a function, getNumberExplanation(), that describes a number passed to it. If there's no explanation available, it returns null:

<?php

getNumberExplanation(8); // null

// There are explanations only for the following numbers
getNumberExplanation(666); // 'devil number'
getNumberExplanation(42);  // 'answer for everything'
getNumberExplanation(7);   // 'prime number'