完成效果圖如下： 
PHP 簡單電腦
實作的功能：
1.簡單的加減乘除和取餘；
2.判别輸入是否為空或不為數字，并彈出提示框給與提示；
操作過程：
建立一個jsq.php，直接把代碼貼進去打開網站就可以了；
也就是說，PHP既可以做前端，也可以做背景的事；
<html>
<head>
<meta charset="UTF-8">
<title>簡單電腦</title>
</head>
<body>
<?php
error_reporting(E_ALL & ~E_NOTICE);
if($_POST['num1'] == "")
echo "<script>alert('第一個數字不能為空')</script>";
elseif(!is_numeric($_POST['num1']))
echo "<script>alert('第一個數字不為數字')</script>";
if($_POST['num2'] == "")
echo "<script>alert('第二個數字不能為空')</script>";
elseif(!is_numeric($_POST['num2']))
echo "<script>alert('第二個數字不為數字')</script>";
$sum = "";
$fuhao = $_POST['fuhao'];
if ($fuhao == '+')
$sum = $_POST['num1'] + $_POST['num2'];
if ($fuhao == '-')
$sum = $_POST['num1'] - $_POST['num2'];
if ($fuhao == '*')
$sum = $_POST['num1'] * $_POST['num2'];
if ($fuhao == '/')
$sum = $_POST['num1'] / $_POST['num2'];
if ($fuhao == '%')
$sum = $_POST['num1'] % $_POST['num2'];
?>
<table width="400" align="center">
<form action="jsq.php" method="post">
<caption><h1>簡單電腦</h1></caption>
<tr>
<td>
<input type="text" size="5" name="num1" value="<?php echo $_POST['num1'] ?>"/>
</td>
<td>
<select name="fuhao">
<option value="+"> + </option>
<option value="-"> - </option>
<option value="*"> * </option>
<option value="/"> / </option>
<option value="%"> % </option>
</select>
</td>
<td>
<input type="text" name="num2" size="5" value="<?php echo $_POST['num2'] ?>"/>
</td>
<td>
=
</td>
<td>
<input type="text" size="5" value="<?php echo $sum; ?>"/>
</td>
<tr align="center">
<td>
<input type="submit" value="計算" name="submit">
</td>
</tr>
</form>
</table>
</body>
</html> ![php寫一個簡潔的登入頁面[圖]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)