How do I print every i'th letter of an array?

skodborg

Hello! 🙂

Here's the thing. During next week, I'll be writing a school-project on encryption, which means the teacher will hand me an encrypted text and tell me to figure out what the original message was

As you may have guesssed already, that'll require an awful lot of systematic approach and testing, which I've tried doing it manually in Microsoft Word, but that's just not working properly and effective enough, and there's a rather high chance of failing at some point

I've been interested in PHP and website-coding a few years back, and thought today that it might come in handy just now! Although, seeing as it has been quite a few years since I coded anything last, I'd love some help coding this tool, or even better, working scripts

The idea was, that if I had a text consisting of like 1000 random letters, shortened down to 15 for illustration, I could pop the text in a HTML text box, and let PHP do the work

The result should be something like this

My random encrypted text: ABCDEFGHIJKLMNO

The PHP script should then split it up and print it out in a number of rows, chosen by me

If I want three rows, the result should be:

Row1: A D G J M
Row2: B E H K N
Row3: C F I L O

If I chose 5 rows, it would be

Row1: AFK
Row2: BGL
Row3: CHM
Row4: DIN
Row5: EJO

I figured I could use the functions str_split(); to split up the encrypted text, and then some sort of $i = 0, print variable, $i += (some chosen number, eg. 3 or 5 as above)

I found this small script, the idea is the same, except I want to decide the number $i, and I want it to work with letters, so count(); probably doesn't work

for ($i = 0; $i < count($array1); $i += 2) 
    echo $array1[$i];

Perhaps array_filter(); somehow?

I'd really love some help, thanks in advance

Skodborg

laserlight

skodborg wrote:
I found this small script, the idea is the same, except I want to decide the number $i, and I want it to work with letters, so count(); probably doesn't work

$i is the index, so you would want to keep it as that. What you want to do is make the increment of 2 a variable. Instead of count, use strlen.

skodborg

Yeah, making the increment a variable, that was what I meant, believe it or not :$ Guess I went a little too fast wording that

Anyway, strlen();? Isn't that a function used to return the length of a string?

What I want is, to be able to list every i'th value in the array

Array
(
[0] => A
[1] => B
[2] => C
[3] => D
[4] => E
[5] => F
[6] => G
[7] => H
[8] => I
[9] => J
[10] => K
[11] => L
[12] => M
[13] => N
[14] => O
)

say I'd increase $i with 3 every time, I want the script to only return

[0] => A
[3] => D
[6] => G
[9] => J
[12] => M

If the strlen(); is in fact the string length, as I recall, then I think you misunderstood me, if you're sure it's doable with strlen();, would you explain me how please?

bradgrafelman

skodborg;10967951 wrote:
say I'd increase $i with 3 every time, I want the script to only return

[0] => A
[3] => D
[6] => G
[9] => J
[12] => M

Doesn't your code above already do that?

$array1 = range('A', 'O');

for ($i = 0; $i < count($array1); $i += 3) 
    echo "[$i] => {$array1[$i]}\n";

output:

[0] => A
[3] => D
[6] => G
[9] => J
[12] => M

skodborg;10967951 wrote:
If the strlen(); is in fact the string length, as I recall, then I think you misunderstood me, if you're sure it's doable with strlen();, would you explain me how please?

I believe laserlight was assuming that the input was a string instead of an array since you referred to "every ith letter" rather than "every ith element in an array of letters."

laserlight

skodborg wrote:
Anyway, strlen();? Isn't that a function used to return the length of a string?

Yes.

skodborg wrote:
If the strlen(); is in fact the string length, as I recall, then I think you misunderstood me, if you're sure it's doable with strlen();, would you explain me how please?

If I misunderstood you, then you need to explain why you wrote that you "want it to work with letters, so count(); probably doesn't work", yet you think strlen will not suffice as a substitute for count when working with strings.

Basically, I expect that you will use nested loops: the outer loop will loop over the rows, and the inner loop will loop over each row, printing the characters one by one.

skodborg

Okay great, it works just as I want it to now!

Apparently, all I needed was indeed that code I posted in the beginning

$array1 = range('A', 'O'); 

for ($i = 0; $i < count($array1); $i += 3) 
    echo "[$i] => {$array1[$i]}\n";

Thanks, both of you, I appreciate the help!
You've saved me for hours of mindless work

laserlight

Good to see that. Here is how I might have done it:

<?php

$ciphertext = 'ABCDEFGHIJKLMNO';
$ciphertext_len = strlen($ciphertext);

$num_rows = 1;
if (isset($_GET['n']))
{
    $num_rows = (int)$_GET['n'];
    if ($num_rows < 1)
    {
        $num_rows = 1;
    }
}

for ($i = 0; $i < $num_rows; ++$i)
{
    echo 'Row ' . ($i + 1) . ': ';
    for ($j = $i; $j < $ciphertext_len; $j += $num_rows)
    {
        echo $ciphertext[$j];
    }
    echo '<br \>';
}