PHP decimal to binary conversion without decbin()

问题

I'm trying to make decimal to binary convertor without using decbin() function. I tried smth like this (which is ok but it needs to be reversed):

    $dec=101;
    while ($dec>=1){
    $bin = $dec % 2;
    $dec = round($dec/2, 0, PHP_ROUND_HALF_DOWN);
    print "$bin";
    }// output:1010011

How could I reverse the output to 1100101? Thanks in forward. :)

回答1:

To convert a decimal integer to binary, repeatedly divide it by 2 — using integer division — until it becomes 0. The remainders at each step, which are 0s and 1s, represent the binary number, when strung together in the reverse order in which they were generated.

    <?php
function dec2bin_i($decimal_i)
{
 bcscale(0);

 $binary_i = '';
 do
  {
   $binary_i = bcmod($decimal_i,'2') . $binary_i;
   $decimal_i = bcdiv($decimal_i,'2');
  } while (bccomp($decimal_i,'0'));

 return($binary_i);
}
?>

Test case

<?php
echo dec2bin_i('36893488147419103232'); //2^65
?>

Output: A 1 followed by 65 zeros:

100000000000000000000000000000000000000000000000000000000000000000

回答2:

There is a function to reverse a string strrev

$dec=101;
$binStr = '';
while ($dec>=1){
    $bin = $dec % 2;
    $dec = round($dec/2, 0, PHP_ROUND_HALF_DOWN);
    $binStr .= $bin;
}
$binStr = strrev($binStr);
echo $binStr;

回答3:

try this:

     $dec = 101;
     $bos = NULL;
     while ($dec>=1){ $bin = $dec % 2; $dec = round($dec/2, 0, 
     PHP_ROUND_HALF_DOWN); 
    $bos .= $bin;
     }
    echo strrev($bos);

来源：https://stackoverflow.com/questions/25017724/php-decimal-to-binary-conversion-without-decbin