PHP: creating a for loop with dynamic Variables - php

Question

I'm trying to slim down the code:
I want to make a for loop out of this part, but it wouldn't work.
$line1 = $frage1[0] . '|' . $frage1[1] . '|' . $frage1[2] . '|' . $frage1[3];
$line2 = $frage2[0] . '|' . $frage2[1] . '|' . $frage2[2] . '|' . $frage2[3];
$line3 = $frage3[0] . '|' . $frage3[1] . '|' . $frage3[2] . '|' . $frage3[3];
$line4 = $frage4[0] . '|' . $frage4[1] . '|' . $frage4[2] . '|' . $frage4[3];
$line5 = $frage5[0] . '|' . $frage5[1] . '|' . $frage5[2] . '|' . $frage5[3];
This is my attempt:
for ($i=1; $i<6; $i++){
${line.$i} = ${frage.$i}[0] . '|' . ${frage.$i}[1] . '|' . ${frage.$i}[2] . '|' . ${frage.$i}[3];
}
EDIT:
This is the solution that works (just so simple :-p):
for ($i=1; $i<18; $i++){
${"line".$i} = implode("|", ${"frage".$i});
fwrite($antworten, ${"line".$i});
}

Answer 1

for ($i=1; $i<6; $i++){
$line[$i] = $frage[0] . '|' . $frage[1] . '|' . $frage$i[2] . '|' . $frage$i[3];
}
This will insert the same thing you posted abov e in line 1 to 6. Is this what you are looking for?!

Answer 2

for ($i=1; $i<6; $i++){
${"line$i"} = ${"frage$i"}[0] . '|' . ${"frage$i"}[1] . '|' . ${"frage$i"}[2] . '|' . ${"frage$i"}[3];
}
That works too!

Answer 3

TL;DR
You might find the documentation on variable variables useful but it looks like the problem is that PHP cannot handle the unquoted string inside your curly brackets.
So instead of ${frage.$i} you need ${"frage$i"}.
Another Approach
However, this is probably not the clearest way to solve this problem. It certainly gives me a bit of a headache trying to work out what this code is trying to do. Instead I would recommend adding all of your $frage to an array first and then looping as follows:
$lines = array();
$frages = array($frage1, $frage2, $frage3, $frage4, $frage5)
foreach($frages as $frage) {
$lines[] = join('|', $frage);
}
Note in particular that you can use join to concatenate each $frage with a | inbetween each, rather than doing this concatenation manually. You could always use [array_slice][2] if you really did only want the first 4 elements of the array to be joined.
If you have a significant number of $frage variables and don't want to add them to an array manually then:
$frages = array();
for($i = 1; $i < x; $i++) {
$frages[] = ${"frage$i"}
}
If you really need each $line variable rather than an array of lines, then you can use extract although this will give you variables like $line_1 rather than $line1:
extract($lines, EXTR_PREFIX_ALL, "line")
However, I would recommend taking a serious look at why you have these numbered $frage being generated and why you need these numbered $line as your output. I would be very surprised if your code could not be re-factored to just use arrays instead, which would make your code much simpler, less surprising and easier to maintain.