มี error เมื่อเปลี่ยนมาใช้ php7 ครับ Warning: A non-numeric value encountered in

$var = 'b500';// non numeric;
echo ($var + 1);// warning error.


if (is_numeric($var)) {
    echo ($var + 1);
} else {
    echo '$var ไม่เป็นตัวเลข!';
}

<input name="d_s_prb" type="text" id="d_s_prb" autocomplete="on" size="2" maxlength="2" value="" 
		onchange="document.getElementById('d_e_prb').value=document.getElementById('d_s_prb').value" OnKeyPress="return chkNumber(this)"/> -
		<input name="m_s_prb" type="text" id="m_s_prb" autocomplete="on" size="2" maxlength="2" value=""
		onchange="document.getElementById('m_e_prb').value=document.getElementById('m_s_prb').value" OnKeyPress="return chkNumber(this)"/> -
		<input name="y_s_prb" type="text" id="y_s_prb" autocomplete="on" size="4" maxlength="4" value="" OnKeyPress="return chkNumber(this)"/>

$prb_s = ($y_s_prb-543).'-'. $m_s_prb.'-'.$d_s_prb;