Starting from the other answers, I came up with a solution that is more comfortable for me:
$var1[]=$var2[]="1";
$var1[]="2";
$var2[]="3";
$var1[]=$var2[]="4";
$var1[]=$var2[]="5";
$var1=implode("",$var1);
$var2=implode("",$var2);
//$var1=1245
//$var2=1345
1
solved Concatenate 2 vars simultaniously