working properly in php 5.6 But I face some problem when I try to run that same code in php 7+

Question

I want to Convert my some code Mysql to Mysqli. Because my code working properly in php 5.6 But I face some problem when I try to run that same code in php 7+. But I face some problem to convert this code. I want to Convert my some code Mysql to Mysqli. Because my code working properly in php 5.6 But I face some problem when I try to run that same code in php 7+. But I face some problem to convert this code. my code is:

    <?php
   error_reporting(E_ALL ^ E_DEPRECATED);

 $dbname = "hrleave";
$dbhost = "localhost";
$dbuser = "hrleave";
$dbpass = "11111";

function connectdb(){
global $dbname, $dbuser, $dbhost, $dbpass;

$conms = @mysql_connect($dbhost,$dbuser,$dbpass); 
//print($conms);
if(!$conms) return false;
$condb = @mysql_select_db($dbname);
if(!$condb) return false;
return true;
}



 function attempt($username, $password)
 {
 $mdpass = md5($password);
 $data = mysql_fetch_array(mysql_query("SELECT COUNT(*) FROM users WHERE username='".$username."' and password='".$mdpass."'"));

if ($data[0] == 1) {
    # set session
    $_SESSION['username'] = $username;
    return true;
} else {
    return false;
}
}


 function attemptadmin($username, $password)
  {
 $mdpass = md5($password);
 $data = mysql_fetch_array(mysql_query("SELECT COUNT(*) FROM admins WHERE username='".$username."' and password='".$mdpass."'"));

if ($data[0] == 1) {
    # set session
    $_SESSION['adminname'] = $username;
    return true;
} else {
    return false;
}
}



 function is_user()
{
if (isset($_SESSION['username']))
    return true;
}
function is_admin()
{
if (isset($_SESSION['adminname']))
    return true;
 }

 function redirect($url)
 {
header('Location: ' .$url);
exit;
 }

 ?>