php - multiple select with different values (security easier method) - php

Question

I don't think this is a duplicate, I only found fairly similar questions.
I have 4 checkboxes and I want to make sure they are different, but I think my "if" is a mess. Let's imagine I have 20 select boxes, then I'd have an endless "if" (option1!=option2...option20, it'd be a really long "if").
How can I simplify this? A while loop or something?
Here is what I have:
PHP check it, then save it:
if(($option1!=$option2 and $option1!=$option3 and $option1!=$option4)
and ($option2!=$option1 and $option2!=$option3 and $option2!=$option4)
and ($option3!=$option1 and $option3!=$option2 and $option3!=$option4)
and ($option4!=$option1 and $option4!=$option2 and $option4!=$option3)) {
//insert it to database if everything is okay...
HTML:
<select name="option1">
<option value="">Choose one</option>
<option value="1">Option A</option>
<option value="2">Option B</option>
<option value="3">Option C</option>
<option value="4">Option D</option>
...
</select>
<select name="option2">
<option value="">Choose one</option>
<option value="1">Option A</option>
<option value="2">Option B</option>
<option value="3">Option C</option>
<option value="4">Option D</option>
...
</select>
<select name="option3">
<option value="">Choose one</option>
<option value="1">Option A</option>
<option value="2">Option B</option>
<option value="3">Option C</option>
<option value="4">Option D</option>
...
</select>
<select name="option4">
<option value="">Choose one</option>
<option value="1">Option A</option>
<option value="2">Option B</option>
<option value="3">Option C</option>
<option value="4">Option D</option>
...
</select>

Answer 1

If you have 20 select dropdown lists with all of them have name attributes in chronological order, like name='option1', name='option2', ... , name='option20', then you should use a for loop like this:
$numSelects = 20;
$selectValues = array();
$differentValues = true;
for($i = 1; $i <= $numSelects; ++$i){
if(in_array($_POST['option'.$i], $selectValues)){
$differentValues = false;
break;
}
$selectValues[] = $_POST['option'.$i];
}
if($differentValues){
// all the selected values are different
}else{
// selected values are not different
}
$numSelects is the number of select dropdown lists in your code, so you need to change this value as per your code. And what this for loop here does is, in each iteration of for loop it checks whether the user's selected value exists in $selectValues array or not, and if the value already exists in the array then it will disable $differentValues flag and break out from the loop. Moreover, in each iteration it appends user's selected value to $selectValues array. After coming out of the loop, you can check whether all submitted values are different or not, based on the status of $differentValues flag.

Answer 2

You could do it like this using array_unique(), you could build on it to know which key is missing to show an error in the right place. It also allows you to define which post keys your expecting to check/count.
<?php
$_POST = [
'name' => 'Steve McQueen',
'csrf' => 'y53zmSV0LhhjcjEg',
'option1' => '1',
'option2' => '3',
'option3' => '2',
'option4' => '1'
];
$expected = [
"option1",
"option2",
"option3",
"option4"
];
$result = [];
foreach ($expected as $key) {
$result[$key] = isset($_POST[$key]) ? $_POST[$key] : null;
}
$check = array_unique($result);
if (count($check) !== count($expected)) {
echo 'Please only select unique choices from the options';
} else {
echo 'All good!';
}