如何在函数内部使用switch语句来更改PHP中的变量？

Question

I'm trying to write a PHP RGB-to-HEX converter and I'm trying to use a function to convert RGB numbers into letters if they're between 10 and 15 (and no, I can't use the "dechex()" function). This is how I have it coded right now:

function convToHex(&$hexInt)
{
    switch($hexInt){
        case 10:
            $hexInt = "A";
            break;
    }
}

//create six hexadecimal variables for "hexMain"

$hex1 = intval($r / 16);
$hex2 = $r % 16;
$hex3 = intval($g / 16);
$hex4 = $g % 16;
$hex5 = intval($b / 16);
$hex6 = $b % 16;

$rgb = "#" . $r . $g . $b;

echo convToHex($hex1);

The problem is that when I try to echo it, the value just comes up as 0. What would be the best way to convert "$hex1", "$hex2", and so-on without using "dechex()"?

Answer 1

You need to return the value ($hexInt in this case) in your function. Then, there's no need for working with a reference.

function convToHex($hexInt) {
    // do things
    return $hexInt;
}

echo convToHex($hexInt);

Answer 2

Your problem is in this line:

echo convToHex($hex1);

If you want to pass by reference, then you need to call the function to alter the variable, then echo it (since the function won't return the value that it alters), eg

convToHex($hex1);
echo $hex1;

...also, any reason not to use something like:

function rgb2hex($r, $g, $b) {
  return sprintf("#%02X%02X%02X", $r, $g, $b);
}

or, if you want something closer to your original logic:

function rgb2hex($r, $g, $b) {
  // takes ints $r, $g, $b in the range 0-255 and returns a hex color string
  $hex_digits = "0123456789ABCDEF";
  $hex_string = "";

  $hex_string .= substr($hex_digits, $r / 16, 1);
  $hex_string .= substr($hex_digits, $r % 16, 1);
  $hex_string .= substr($hex_digits, $g / 16, 1);
  $hex_string .= substr($hex_digits, $g % 16, 1);
  $hex_string .= substr($hex_digits, $b / 16, 1);
  $hex_string .= substr($hex_digits, $b % 16, 1);

  return "#" . $hex_string;
}

to use either of these would involve something like:

$r = 12;
$g = 234;
$b = 45;

$hex_string = rgb2hex($r, $g, $b);
echo $hex_string . "\n";