为什么这个总是第一个不合法？

<code>
<form method="post">
    <input type="text" name="name">
    <input type="text" name="name2">
    <button type="submit">提交</button>
</form>
<?php
$reg1='/^[1-9]\d{5,9}$/i';
$reg2='/\w{30,100}/';
$a=$_POST['name'];
$b=str_replace(" ","",$_POST['name2']);
if(preg_match($reg1, $a)){
    $nm=1;
}else{
    $nm=2;
}
if(preg_match($reg2, $b)){
    $cm=1;
}else{
    $cm=2;
}
if($nm=2){
    echo "1buhefa";
}else if($cm=2){
    echo "2buhefa";
}else{
    echo "yes";
}

?>
</code>

<code>
<form method="post">
    <input type="text" name="name">
    <input type="text" name="name2">
    <button type="submit">提交</button>
</form>
<?php
$reg1='/^[1-9]\d{5,9}$/i';
$reg2='/\w{30,100}/';
$a=$_POST['name'];
$b=str_replace(" ","",$_POST['name2']);
if(preg_match($reg1, $a)){
    $nm=1;
}else{
    $nm=2;
}
if(preg_match($reg2, $b)){
    $cm=1;
}else{
    $cm=2;
}
if($nm=2){
    echo "1buhefa";
}else if($cm=2){
    echo "2buhefa";
}else{
    echo "yes";
}

?>
</code>