php form study -> add form required fields

Add form validation 

<?php
// define variables and set to empty values
$nameErr = $emailErr = $genderErr = $websiteErr = "";
$name = $email = $gender = $comment = $website = "";

if ($_SERVER["REQUEST_METHOD"] == "POST") {
  if (empty($_POST["name"])) {
    $nameErr = "Name is required";
  } else {
    $name = test_input($_POST["name"]);
  }

  if (empty($_POST["email"])) {
    $emailErr = "Email is required";
  } else {
    $email = test_input($_POST["email"]);
  }

  if (empty($_POST["website"])) {
    $website = "";
  } else {
    $website = test_input($_POST["website"]);
  }

  if (empty($_POST["comment"])) {
    $comment = "";
  } else {
    $comment = test_input($_POST["comment"]);
  }

  if (empty($_POST["gender"])) {
    $genderErr = "Gender is required";
  } else {
    $gender = test_input($_POST["gender"]);
  }
}
?>

  紅色的字體是新增的....

   這邊使用了  empty 這個function 來判斷  $_POST["name"] 是不是空字串...

  如果是空字串的話.....  就把 $nameErr assign 成 "Name is required"

接下來再修改code...讓  $nameErr 秀在網頁上...

<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">

Name: <input type="text" name="name">
<span class="error">* <?php echo $nameErr;?></span>
<br><br>
E-mail:
<input type="text" name="email">
<span class="error">* <?php echo $emailErr;?></span>
<br><br>
Website:
<input type="text" name="website">
<span class="error"><?php echo $websiteErr;?></span>
<br><br>
Comment: <textarea name="comment" rows="5" cols="40"></textarea>
<br><br>
Gender:
<input type="radio" name="gender" value="female">Female
<input type="radio" name="gender" value="male">Male
<span class="error">* <?php echo $genderErr;?></span>
<br><br>
<input type="submit" name="submit" value="Submit"> 

</form>

紅色字體是新增的.....

他會秀出   *  這個符號.... 後面再加上   <?php echo $emailErr;?>

利用echo function 秀出字串.....

執行畫面如下.....如果你沒有在 Name 那個欄位上面輸入 任何的文字...

當你按下 Submit ....他就會去判斷是不是空字串...如果是空字串...就會把 $NameErr 

assign  'Name is required'...然後就會秀出來..

Reference : http://www.w3schools.com/php/php_form_required.asp