PHP: Logic Type

Besides arithmetic operators, you'll also know comparison operators from school. For example, 5 > 4. It sounds like a question, "Is 5 greater than 4?" The answer is "yes". In other cases, the answer may be "no" (e.g., for 3 < 1).

Comparison operators aren't restricted to numbers. You can put them in almost anything, e.g., strings. Every time we visit a website, it compares the username and password we've entered with those in the database. And they'll let us in if we have them (authentication).

Programming languages have borrowed all the comparison operators from math virtually unchanged. The only major change concerns the equality and inequality operators. In math, the usual equal sign is =, but this is rare in programming. In many languages, the symbol = is used to assign values to variables, so you need to use == or === for comparison.

List of comparison operations:

• < less than
• <= less than or equal to
• > more than
• >= greater than or equal to
• === equal to
• !== not equal to

A tiny note: for equality and inequality, there's also == and !=, neither of which we'll use because of the possible risks. We'll discuss it later.

A logical operation like 5 > 4 or $password === $text is an expression, and its result is a special value, true or false. This is a new data type for us - bool. It has only these two values.

<?php

$result = 5 > 4;
print_r($result); // => true
print_r('one' !== 'one'); // => false

Along with strings and integers and rational numbers, the boolean type is one of the most primitive data types in PHP.

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Try writing a primitive function that takes a child's age as input and decides whether they are a baby or not. Babies are defined as children under a year old:

<?php

function isInfant($age)
{
    return $age < 1;
}

We're taking advantage of the fact that any operation is an expression, so the only line of the function is "return the value that results from comparison $age < 1».

Depending on the argument that came in, the comparison will either be (true) or (false), and return will return that result.

Let's call the function and display the result. You should usevar_dump(), to output bool, not print_r():

<?php

function isInfant($age)
{
    return $age < 1;
}

var_dump(isInfant(3));

bool(false)

Now, perform the check on a child who's six months old:

<?php

var_dump(isInfant(0.5));

bool(true)

Instructions

Write an isPensioner() function that takes age as a single argument and checks if it's over retirement age For the purposes of this exercise, retirement age is considered to be 60 years or over.

Call examples:

<?php

isPensioner(75); // true
isPensioner(18); // false

Definitions

• bool is a data type with two possible values: true and false.