逻辑弄错，难怪想不明白，是满足while条件才执行语句，而不是一直循环到满足while条件！
2016-03-18
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>php语句结束符</title>
</head>
<body>
<p>
<?php
echo "欢迎同学们！";
echo "Welcome" . " to imooc!";
echo 1+2+3+4+5;
//开学欢迎仪式 ?>
</p>
</body>
</html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>php语句结束符</title>
</head>
<body>
<p>
<?php
echo "欢迎同学们！";
echo "Welcome" . " to imooc!";
echo 1+2+3+4+5;
//开学欢迎仪式 ?>
</p>
</body>
</html>
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>php语句结束符</title>
</head>
<body>
<p>
<?php
echo "欢迎同学们！";
echo "Welcome" . " to imooc!";
echo 1+2+3+4+5;
?>
</p>
</body>
</html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>php语句结束符</title>
</head>
<body>
<p>
<?php
echo "欢迎同学们！";
echo "Welcome" . " to imooc!";
echo 1+2+3+4+5;
?>
</p>
</body>
</html>
2016-03-18
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>字符串</title>
</head>
<body>
<p>
<?php echo "Hi"."imooc"; ?>
</p>
</body>
</html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>字符串</title>
</head>
<body>
<p>
<?php echo "Hi"."imooc"; ?>
</p>
</body>
</html>
2016-03-18
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>计算表达式</title>
</head>
<body>
<p>
<?php echo 12*3;?>
</p>
</body>
</html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>计算表达式</title>
</head>
<body>
<p>
<?php echo 12*3;?>
</p>
</body>
</html>
2016-03-18