php简单计算器提供全部

<b>简单计算器</b><br>
<form method="post" action="cyg.php">
结果:<input type="text" name="sum" id="sum" size="15"><br>
数字1:<input type="text" name="num1" size="10"><br>
运算符:<select name="sub">
<option value="+">+</option>
<option value="-">-</option>
<option value="*">*</option>
<option value="/">/</option>
</select>
<br>
数字2:<input type="text" name="num2" size="10"><br>
<input type="submit" value="计算">&nbsp;
<input type="reset" value="重置">
</form>
<?php
if(!empty($_POST['num1'])){
  //如果不为空的情况下
$num1 = $_POST['num1'];//获取第一个输出的值
$num2 = $_POST['num2'];//获取第二个输出的值
$sub = $_POST['sub'];//获取是+还是-还是*还是除
$sum=0;
switch($sub){
case "+":
  $sum=$num1+$num2;
break;
case "-":
  $sum=$num1-$num2;
break;
case "*":
  $sum=$num1*$num2;
break;
case "/":
  $sum=$num1/$num2;
break;
}
echo "<script>alert('计算结果为:".$sum."');</script>";
echo "<script>document.getElementById('sum').value='".$sum."'</script>";
}
?>