calculate binary to decimal manually

问题

assuming I have a function to manually calculate decimal from binary number
*up to four characters(binary)
*assuming you can only input 0 and 1 character

below code works perfectly

function bin_to_dec($bin) {
$bin = str_split($bin);
$bin = array_reverse($bin);

$i = 0;
$dec = 0;
foreach($bin as $values) {
    $ans = $values * pow(2, $i);
    $dec += $ans;
    $i++;
}

return $dec;

}

$bin = 1010 //4
$bin = 1 //1
$bin = 0 //0

assuming if you cannot use function strrev(), str_split(), array_reverse(), how would you convert binary to decimal manually?

回答1:

Well, have you tried the built-in bindec function ?

var_dump(bindec(1010)); // int(10)
var_dump(bindec(1)); // int(1)
var_dump(bindec(101010)); // int(45)

Beware though, this function is meant to be used with strings and can give strange results for ints beginning with 0 :

var_dump(bindec(0101)); // int(0)
var_dump(bindec("0101")); // int(5)

回答2:

http://php.net/manual/en/function.bindec.php

Example bindec() example

<?php
echo bindec('110011') . "\n";
echo bindec('000110011') . "\n";

echo bindec('111');
?>
The above example will output:

51
51
7

回答3:

Try the bindec() function.

$ret_val = bindec("10001101");

this is one simple way,otherwise you can use...

    <?php
function strev($y)
{
for ($x = strlen($y)-1; $x>=0; $x--) {
       $y .= $y[$x];
       $y[$x] = NULL;
}
return $y;
}
function bintodec($str){
    $dec=0;
    $nstr=$str;
    $nstr=strev($nstr);
    for($i=0;$i<strlen($str);$i++){
        $val = ($nstr%pow(10,strlen($nstr)-1)) * pow(2, $i);
        $dec += $val;
        $nstr=floor($nstr/10);
    }
    return $dec;
}
echo bintodec("1111010");
?>

回答4:

Just had to solve this for a student.

Split the string representation into digits
Reverse the digits
Initiate our result
Iterate over all the digits, adding 2 in the power of the index if the digit is a 1

Using the fact that each digit in binary adds 2 in the power of the digits index to the result.

Binary 11 is equal to 2^0 + 2^1 = 3

function binaryToDecimal($str) {
    $digits = str_split($str);
    $reversed = array_reverse($digits);
    $res = 0;

    for($x=0; $x < count($reversed); $x++) {
        if($reversed[$x] == 1) {
            $res += pow(2, $x);
        }
    }

    return $res;
}

来源：https://stackoverflow.com/questions/41760989/calculate-binary-to-decimal-manually

标签

php

binary

decimal