converting hexadecimal to decimal php - php

Question

I have to convert hexadecimal to decimal with PHP (without using hexdec) for my homework, but my code does not convert properly.
For example, when I use the function HexToDez ("1F4");, the answer should be 500, not 1.
Why is it not working?
the code
<?php
function Replace ($i)
{
switch (strToLower ($i))
{
case "a" : return 10;
case "b" : return 11;
case "c" : return 12;
case "d" : return 13;
case "e" : return 14;
case "f" : return 15;
default : return $i;
}
}
function HexToDez($i) # 1F4
{
$input=$i;
$num=strlen ($input) ;
$pos=0;
$output="";
$hochzahl="";
while($pos<$num)
{
$mid = substr ($input, $pos, 1);
$pos++;
return $end=Replace ($mid);
}
while ($end != 0){
$zahl = $input%10;
$output += $zahl*pow(16, $hochzahl);
$end = $end/10;
$hochzahl++;
}
echo $output;
}
?>

Answer 1

here is "classic" algorithm for you to consider, check the comments:
function HexToDez($s) {
$output = 0;
for ($i=0; $i<strlen($s); $i++) {
$c = $s[$i]; // you don't need substr to get 1 symbol from string
if ( ($c >= '0') && ($c <= '9') )
$output = $output*16 + ord($c) - ord('0'); // two things: 1. multiple by 16 2. convert digit character to integer
elseif ( ($c >= 'A') && ($c <= 'F') ) // care about upper case
$output = $output*16 + ord($s[$i]) - ord('A') + 10; // note that we're adding 10
elseif ( ($c >= 'a') && ($c <= 'f') ) // care about lower case
$output = $output*16 + ord($c) - ord('a') + 10;
}
return $output;
}
echo HexToDez("1F4"); // outputs 500
also, you can use intval function to do the same, just convert your number into hex representation, like 0x###
function HexToDez($s) {
return intval('0x'.$s, 16);
}