I have a small programm where i take in a users Bitcoin address as input and than insert it into mysql database.

for the input form i have this

<form class="" action="submit.php" method="post">
    <input type="text"  name="address" placeholder="your Bitcoin address">
    <button type="submit" name="submit" class="btn btn-info">Submit</button>
  </form>
the submit php looks like this

include_once 'db.php';

$eth = mysqli_real_escape_string($conn,$_POST['address']);


$sql = "INSERT INTO address(address) VALUES('$eth');";
mysqli_query($conn, $sql);

header("Location: ../bitcoin/transfer.php");
What i want to do is

user inputs bitcoin address and clicks submit button

which than validates the bitcoin address and if address is valid- he can click submit button and gets redirected to a different part of my site- and if adress is valid it gets added to mysql database.

If input isnt valid - display error message

Im using php for everything

And the code to validate if bitcoin address is valid is this

<?php

function checkAddress($address)
{
    $origbase58 = $address;
    $dec = "0";

    for ($i = 0; $i < strlen($address); $i++)
    {
        $dec = bcadd(bcmul($dec,"58",0),strpos("123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz",substr($address,$i,1)),0);
    }

    $address = "";

    while (bccomp($dec,0) == 1)
    {
        $dv = bcdiv($dec,"16",0);
        $rem = (integer)bcmod($dec,"16");
        $dec = $dv;
        $address = $address.substr("0123456789ABCDEF",$rem,1);
    }

    $address = strrev($address);

    for ($i = 0; $i < strlen($origbase58) && substr($origbase58,$i,1) == "1"; $i++)
    {
        $address = "00".$address;
    }

    if (strlen($address)%2 != 0)
    {
        $address = "0".$address;
    }

    if (strlen($address) != 50)
    {
        return false;
    }

    if (hexdec(substr($address,0,2)) > 0)
    {
        return false;
    }

    return substr(strtoupper(hash("sha256",hash("sha256",pack("H*",substr($address,0,strlen($address)-8)),true))),0,8) == substr($address,strlen($address)-8);
}

?>
I just dont know how to put this together into a working project