I have very little programming experience but I am going over a php book and this block of code is confusing me.
If rand generates a random integer, how does this program use ABCDEFG in the array.
Can you please explain the program thank you. I know what the result is, I am just not sure how it get it.
<?php
$array = '123456789ABCDEFG';
$s = '';
for ($i=1; $i < 50; $i++) {
$s.= $array[rand(0,strlen($array)-1)]; //explain please
}
echo $s;
?>
It's using the array index so $array[11] would equal 'C'. rand() takes a range - in your example that's from 0 to strlen($array)-1 which is the length of the string, minus 1 since it's a 0 based index.
Break it down into parts:
strlen($array) - returns the length of the string in $array, which would be 17
strlen($array) - 1 => 16
rand(0, 16) - generate a random number between 0 and 16
$array[$random_number] - get the $random_number'th element of the array
Its just taking the length of the array with strlen($array). It doesn't matter what is in the string just the length. Then its generating a random number between 0 and the length of the string minus one.
Then it takes whatever character is in that position in the array (so $array[5] would be '6', $array[12] would be 'C', etc) and appending that to string $s. It then has a for loop to repeat it 50 times.
What you end up with is a random string that is 50 characters long and contains the numbers 1-9 and letters A-G.
Related
I'm trying to use CodeIgniter to write up a small program for school which generates a random 'key' every time I click the 'generate' button. Looking to see if there's a way for me to create a function where I can fill up a 14 character array with a random number or letter and then set the array to a variable which I can call upon to display as my generated key.
Any and all help would be much appreciated as I am new to CodeIgniter.
A while back I wrote this function in PHP, it does what it does and gives you some flexibility as well through complexity modifiers, I used a default set of 5 different 'levels' of characters and the length is also variable ofcourse.
I'm just going to chuck it in here and 'try' to explain what is going on as well as I can by comments:
function rsg($length = 10, $complexity = 2) {
//available 'complexity' subsets of characters
$charSubSets = array(
'abcdefghijklmnopqrstuvwxyz',
'ABCDEFGHIJKLMNOPQRSTUVWXYZ',
'0123456789',
'!##$%^&*()_+{}|:">?<[]\\\';,.`~',
'µñ©æáßðøäåé®þüúíóö'
);
// will be filled with subsets from above $charSubsets
$chars = '';
//concact each subset until complexity is reached onto the $chars variable
for ($i = 0; $i < $complexity; $i++)
$chars .= $charSubSets[$i];
//create array containing a single char per entry from the combined subset in the $chars variable.
$chars = str_split($chars);
//define length of array for mt_rand limit
$charCount = (count($chars) - 1);
//create string to return
$string = '';
//idk why I used a while but it won't really hurt you when the string is less than 100000 chars long ;)
$i = 0;
while ($i < $length) {
$randomNumber = mt_rand(0, $charCount); //generate number within array index range
$string .= $chars[$randomNumber]; //get that character out of the array
$i++; //increment counter
}
return $string; //return string created from random characters
}
This is what I currently use and it has satisfied my needs for quite some time now, if anyone reading over this has improvements I'd love to hear them as well!
$a=array(rand(10000000000000, 99999999999999));
is a quick way to get a 14 digit array.
It depends on how random you want it to be. You could specify all characters you want in a $characters string, then just create a string up to $length, picking a random substring of length 1 from the characters string.
What are the requirements?
Do you want it to be as random as possible (This link might be useful)
Are multiple occurrences of one character allowed in one random string?
Here's an example though: PHP random string generator
Is there a term for the idea of storing large numbers as letters? For example let's say I have the (relatively small) number 138201162401719 and I want to shrink the number of characters (I know this does not help with saving disk space) to the fewest possible number of characters. There are 26 letters in the English alphabet (but i count them as 25 since we need a zero letter). If I start splitting up my large number into pieces that are each 25 or less I get:
13, 8, 20, 11, 6, 24, 0, 17, 19
If I then count the numbers of the alphabet a=0, b=1, c=2, d=3... I can convert this to:
NIULGYART
So I went from 15 digits long (138201162401719) to 9 characters long (NIULGYART). This could of course be easily converted back to the original number as well.
So...my first question is "Does this have a name" and my second "Does anyone have PHP code that will do the conversion (in both directions)?"
I am looking for proper terminology so that I can do my own research in Google...though working code examples are cool too.
This only possible if you're considering to store your number before processing as a string. Because you can't store huge number as integers. You will lost the precision (13820116240171986468445 will be stored as 1.3820116240172E+22) so the alot of digits are lost.
If you're considering storing the number as a string this will be your answer:
Functions used: intval, chr and preg_match_all.
<?php
$regex = '/(2[0-5])|(1[0-9])|([0-9])/';
$numberString = '138201162401719';
preg_match_all($regex, $numberString, $numberArray, PREG_SET_ORDER);
echo($numberString . " -> ");
foreach($numberArray as $value){
$character = chr (intval($value[0]) + 65);
echo($character);
}
?>
Demo
This is the result:
138201162401719 -> NIULGYART
Here's how I would do it:
Store the big number as a string and split it into an array of numbers containing one digit each
Loop through the array extract 2-digit chunks using substr()
Check if the number is less than 26 (in which case, it is an alphabet) and add them to an array
Use array_map() with chr() to create a new array of characters from the above array
Implode the resulting array to get the cipher
In code:
$str = '138201162401719';
$arr = str_split($str);
$i = 0; // starting from the left
while ($i < count($arr)) {
$n = substr($str, $i, 2);
$firstchar = substr($n, 0, 1);
if ($n < 26 && $firstchar != 0) {
$result[] = substr($str, $i, 2);
$i += 2; // advance two characters
} else {
$result[] = substr($str, $i, 1);
$i++; // advance one character
}
}
$output = array_map(function($n) {
return chr($n+65);
}, $result);
echo implode($output); // => NIULGYART
Demo.
As an alternative, you could convert the input integer to express it in base 26, instead of base 10. Something like (pseudocode):
func convertBase26(num)
if (num < 0)
return "-" & convertBase26(-num) // '&' is concatenate.
else if (num = 0)
return "A"
endif
output = "";
while (num > 0)
output <- ('A' + num MOD 26) & output // Modulus operator.
num <- num DIV 26 // Integer division.
endwhile
return output
endfunc
This uses A = 0, B = 1, up to Z = 25 and standard place notation: 26 = BA. Obviously a base conversion is easily reversible.
strtr() is a magnificent tool for this task! It replaces the longest match as is traverses the string.
Code: (Demo)
function toAlpha ($num) {
return strtr($num, range("A", "Z"));
}
$string = toAlpha("138201162401719");
echo "$string\n";
$string = toAlpha("123456789012345");
echo "$string\n";
$string = toAlpha("101112131415161");
echo "$string\n";
$string = toAlpha("2625242322212019");
echo "$string";
Output:
NIULGYART
MDEFGHIJAMDEF
KLMNOPQB
CGZYXWVUT
Just flip the lookup array to reverse the conversion: https://3v4l.org/YsFZu
Merged: https://3v4l.org/u3NQ5
Of course, I must mention that there is a vulnerability with converting a sequence of letters to numbers and back to letters. Consider BB becomes 11 then is mistaken for eleven which would traslate to L when converted again.
There are ways to mitigate this by adjusting the lookup array, but that may not be necessary/favorable depending on program requirements.
And here is another consideration from CodeReview.
I have been trying to do the same thing in PHP without success.
Assuming I'm using the 26 letters of the English alphabet, starting with A = 0 down to Z as 25:
I find the highest power of 26 lower than the number I am encoding. I divide it by the best power of 26 I found. Of the result I take away the integer, convert it to a letter and multiply the decimals by 26. I keep doing that until I get a whole number. It's ok to get a zero as it's an A, but if it has decimals it must be multiplied.
For 1 billion which is DGEHTYM and it's done in 6 loops obviously. Although my answer demonstrates how to encode, I'm afraid it does not help doing so on PHP which is what I'm trying to do myself. I hope the algorithm helps people out there though.
*I try to count the unique appearances of a substring inside a list of words *
So check the list of words and detect if in any words there are substrings based on min characters that occur multiple times and count them. I don't know any substrings.
This is a working solution where you know the substring but what if you do not know ?
Theres a Minimum Character count where words are based on.
Will find all the words where "Book" is a substring of the word. With below php function.
Wanted outcome instad:
book count (5)
stor count (2)
Given a string of length 100
book bookstore bookworm booking book cooking boring bookingservice.... ok
0123456789... ... 100
your algorithm could be:
Investigate substrings from different starting points and substring lengths.
You take all substrings starting from 0 with a length from 1-100, so: 0-1, 0-2, 0-3,... and see if any of those substrings accurs more than once in the overall string.
Progress through the string by starting at increasing positions, searching all substrings starting from 1, i.e. 1-2, 1-3, 1-4,... and so on until you reach 99-100.
Keep a table of all substrings and their number of occurances and you can sort them.
You can optimize by specifying a minimum and maximum length, which reduces your number of searches and hit accuracy quite dramatically. Additionally, once you find a substring save them in a array of searched substrings. If you encounter the substring again, skip it. (i.e. hits for book that you already counted you should not count again when you hit the next booksubstring). Furthermore you will never have to search strings that are longer than half of the total string.
For the example string you might run additional test for the uniquness of a string.
You'd have
o x ..
oo x 7
bo x 7
ok x 6
book x 5
booking x 2
bookingservice x 1
with disregarding stings shorter than 3 (and longer than half of total textstring), you'd get
book x 5
booking x 2
bookingservice x 1
which is already quite a plausible result.
[edit] This would obviously look through all of the string, not just natural words.
[edit] Normally I don't like writing code for OPs, but in this case I got a bit interested myself:
$string = "book bookshelf booking foobar bar booking ";
$string .= "selfservice bookingservice cooking";
function search($string, $min = 4, $max = 16, $threshhold = 2) {
echo "<pre><br/>";
echo "searching <em>'$string'</em> for string occurances ";
echo "of length $min - $max: <br/>";
$hits = array();
$foundStrings = array();
// no string longer than half of the total string will be found twice
if ($max > strlen($string) / 2) {
$max = strlen($string);
}
// examin substrings:
// start from 0, 1, 2...
for ($start = 0; $start < $max; $start++) {
// and string length 1, 2, 3, ... $max
for ($length = $min; $length < strlen($string); $length++) {
// get the substring in question,
// but search for natural words (trim)
$substring = trim(substr($string, $start, $length));
// if substring was not counted yet,
// add the found count to the hits
if (!in_array($substring, $foundStrings)) {
preg_match_all("/$substring/i", $string, $matches);
$hits[$substring] = count($matches[0]);
}
}
}
// sort the hits array desc by number of hits
arsort($hits);
// remove substring hits with hits less that threshhold
foreach ($hits as $substring => $count) {
if ($count < $threshhold) {
unset($hits[$substring]);
}
}
print_r($hits);
}
search($string);
?>
The comments and variable names should make the code explain itself. $string would come for a read file in your case. This exmaple would output:
searching 'book bookshelf booking foobar bar booking selfservice
bookingservice cooking' for string occurances of length 4 - 16:
Array
(
[ook] => 6
[book] => 5
[boo] => 5
[bookin] => 3
[booking] => 3
[booki] => 3
[elf] => 2
)
Let me know how you implement it :)
This is my first approximation: unfinished, untested, has at least 1 bug, and is written in eiffel. Well I am not going to do all the work for you.
deferred class
SUBSTRING_COUNT
feature
threshold : INTEGER_32 =5
biggest_starting_substring_length(a,b:STRING):INTEGER_32
deferred
end
biggest_starting_substring(a,b:STRING):STRING
do
Result := a.substring(0,biggest_starting_substring_length(a,b))
end
make_list_of_substrings(a,b:STRING)
local
index:INTEGER_32
this_one: STRING
do
from
a_index := b_index + 1
invariant
a_index >=0 and a_index <= a.count
until
a_index >= a.count
loop
this_one := biggest_starting_substring(a.substring (a_index, a.count-1),b)
if this_one.count > threshold then
list.extend (this_one)
end
variant
a.count - a_index
end
end -- biggest_substring
list : ARRAYED_LIST[STRING]
end
I'm working on something which requires unique ID numbers which are in the format of:
[A-Z][A-Z0-9][A-Z0-9][A-Z0-9][A-Z0-9][A-Z0-9]
And increment as:
AAAAAA, AAAAAB, ... AAAAAZ, AAAAA0, AAAAA1, .. AAAAA9, AAAABA, AAAABB
I know I can increment letters in PHP, but how would I do letters and numbers in such a way?
Special note, baseconvert isn't an option, because it must always be exactly 6 characters and fit the noted format incrementally. Further, baseconvert starts at 0, not A, so if I do start at "621937810" (AAAAAA) the next jump will be after AAAAAZ and on to AAAAB0. It seemed like the quickest solution, but it doesn't work.
you could try base_convert from 36 to 10, increment then 10 to 36. I didn't have any trouble with the larger numbers like ZZZZZW+1, however as it says in the php manual, there could be problems with larger numbers due to float/double precision.
<?php
echo "<pre>";
//orig string
$test = 'ZZZZZW';
//convert from base36 to number.
$test = base_convert($test, 36, 10);
var_dump($test);
//increment
$test++;
var_dump($test);
//convert back (and upper case)
$test = strtoupper(base_convert($test, 10, 36));
var_dump($test);
?>
outputs:
string(6) "ZZZZZW"
string(10) "2176782332"
float(2176782333)
string(6) "ZZZZZX"
example can be see here
Other than that, you can do some custom increment or even check out the base_convert comments in the php manual on converting some larger bases and values.
Edit after clarification:
Taken from the php comments page:
<?php
function intToAlphaBaseN($n,$baseArray) {
$l=count($baseArray);
$s = '';
for ($i = 1; $n >= 0 && $i < 10; $i++) {
$s = $baseArray[($n % pow($l, $i) / pow($l, $i - 1))].$s;
$n -= pow($l, $i);
}
return $s;
}
$base=array_merge(range('A','Z'), range(0,9));
$zero = $base[0];
//an integer number
$r=rand(0, 999999);
echo "$r converts to :".str_pad(intToAlphaBaseN($r,$base), 6, $zero, STR_PAD_LEFT)."\n";
//an integer number
$r++;
echo "$r converts to :".str_pad(intToAlphaBaseN($r,$base), 6, $zero, STR_PAD_LEFT)."\n";
//an integer number
$r++;
echo "$r converts to :".str_pad(intToAlphaBaseN($r,$base), 6, $zero, STR_PAD_LEFT)."\n";
?>
working example
As for incrementing from the string ID, I would suggest either saving the integer value, increment that and convert or write a similar function to convert to integer, increment, convert back. The former probably being easier.
And as far as forcing the same 6 character format, the only time this should be a problem is when you pass the Z99999 which according to your format, is the max.
You are basically describing a 36-ary notation (as opposed to binary, decimal, or hexadecimal). I.e. the last letter represents (int value) mod 36, the second-but last letter represents (value/36)%36. Transform an integer into an array of six numbers from 0 to 35. Then map the resulting values such that 0=A, 25=Z, 26=0 and so on. Incrementing is just achieved by starting with an int value of 0, incrementing it, and transforming it into such a string after each increment. Yea you can probably also set up a 36-ary arithmetic such that you don't waste time between i and i+1, but I'd rather go with a brute force approach like that to begin with.
How can I separate a number and get the first two digits in PHP?
For example: 1345 -> I want this output=> 13 or 1542 I want 15.
one possibility would be to use substr:
echo substr($mynumber, 0, 2);
EDIT:
please not that, like hakre said, this will break for negative numbers or small numbers with decimal places. his solution is the better one, as he's doing some checks to avoid this.
First of all you need to normalize your number, because not all numbers in PHP consist of digits only. You might be looking for an integer number:
$number = (int) $number;
Problems you can run in here is the range of integer numbers in PHP or rounding issues, see Integers Docs, INF comes to mind as well.
As the number now is an integer, you can use it in string context and extract the first two characters which will be the first two digits if the number is not negative. If the number is negative, the sign needs to be preserved:
$twoDigits = substr($number, 0, $number < 0 ? 3 : 2);
See the Demo.
Shouldn't be too hard? A simple substring should do the trick (you can treat numbers as strings in a loosely typed language like PHP).
See the PHP manual page for the substr() function.
Something like this:
$output = substr($input, 0, 2); //get first two characters (digits)
You can get the string value of your number then get the part you want using
substr.
this should do what you want
$length = 2;
$newstr = substr($string, $lenght);
With strong type-hinting in new version of PHP (> PHP 7.3) you can't use substr on a function if you have integer or float. Yes, you can cast as string but it's not a good solution.
You can divide by some ten factor and recast to int.
$number = 1345;
$mynumber = (int)($number/100);
echo $mynumber;
Display: 13
If you don't want to use substr you can divide your number by 10 until it has 2 digits:
<?php
function foo($i) {
$i = abs((int)$i);
while ($i > 99)
$i = $i / 10;
return $i;
}
will give you first two digits