# 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.

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 use`var_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
``````
The exercise doesn't pass checking. What to do? 😶

• Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
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 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.

## Definitions

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

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