Simple calculator program in php using functions

<h2>Simple Calculator</h2><br>

First Number:<input name="n1"value=""><br>

Second Number:<input name="n2"value=""><br>

<input type="submit"name="sub"value="+">

<input type="submit"name="sub"value="-">

<input type="submit"name="sub"value="x">

<input type="submit"name="sub"value="/"><br>

<br>Result:<input type='text'value=" echo$ans;?>"><br>

</form>

if(isset($_POST['sub'])){

$num1=$_POST['n1'];

$num2=$_POST['n2'];

$oprnd=$_POST['sub'];

if($oprnd=="+")

$ans=$num1+$num2;

elseif($oprnd=="-")

$ans=$num1-$num2;

elseif($oprnd=="x")

$ans=$num1*$num2;

else if($oprnd=="/")

$ans=$num1/$num2;

}?>