Why do false statements print nothing rather than 0 in PHP? - php

Question

Here's a simple example:
echo 3==3; // echoes 1
echo 3==2; // should echo 0, yet echoes nothing
I noticed this as I was designing a form which entails a checkbox. When ticked, the checkbox passes a value of 1, when unticked, rather than passing a value of 0 as one would expect, it passes nothing; an undefined boolean so to speak.
I tried solving this with the following code:
$myBool = isset($_POST['myCheckbox']);
However, this doesn't seem to work either.
One solution to passing the checkbox value to $myBool would be to do some if-else conditioning, but I want a more concise solution. Is this possible?

Answer 1

In PHP, every decision makes statement returns a boolean value, either true or false. So, echo 3==3; is a true statement, That's why it returns 1 and echo 3==2; is a false statement, that's why it returns nothing.
But if you want to echo out the associated integer of false (which is 0), then you can use typecasting. Like:
echo (int)(3 == 2);
It will print out 0.

Answer 2

Test Code
// http://php.net/manual/en/language.operators.comparison.php
echo 3==3;
echo "<br>---------------<br>";
echo 3==2;
echo "<br>---------------<br>";
var_dump(3==3);
echo "<br>---------------<br>";
var_dump(3==2);
Output
1
---------------
---------------
boolean true
---------------
boolean false
The reason is for no output is you are trying to echo the boolean "false", which prints nothing.

Answer 3

The statement 3 == 2 evaluates to false, and as noted in the PHP documentation for echo under the examples section, running echo false won't print anything because it's not technically a function. However, you can use var_dump instead.
echo 3 == 2; // no output
echo false; // no output
var_dump(3 == 2); // outputs bool(false)
var_dump(false); // outputs bool(false)

Answer 4

The actual reason for your question about why a statement that evaluates to echo false; prints an empty string, is given in the documentation on strings, in the section about casting to string:
Converting to string
A value can be converted to a string using the (string) cast or the
strval() function. String conversion is automatically done in the
scope of an expression where a string is needed. This happens when
using the echo or print functions, or when a variable is compared to a
string. The sections on Types and Type Juggling will make the
following clearer. See also the settype() function.
A boolean TRUE value is converted to the string "1". Boolean FALSE
is converted to "" (the empty string). This allows conversion back and
forth between boolean and string values.
The reason that you can't test an unchecked checkbox, the way you tried, is that browsers don't send unchecked checkbox states on form submissions.
Typical solutions to this conundrum are:
Keep track of all available checkboxes in the backend and compare them upon receiving a form submission.
Add a hidden field in your HTML form before the actual checkbox, giving it the same name as the checkbox and a value that represents the unchecked state.
<input type="hidden" name="checkbox1" value="0">
<input type="checkbox" name="checkbox1" value="1">
These hidden fields will be submitted upon form submission and will be overwritten by the checkbox value if it is checked1.
1) The values will actually both be send if the checkbox is checked, but PHP will overwrite any earlier received value with a later received value if they have the same parameter name (unless the parameter name represents an array without explicit key names, like name="checkbox[]" instead of name="checkbox[1]").