PHP表单处理：表单数据依赖处理与联动

<form action="process.php" method="post">
  <label for="quantity">货物数量：</label>
  <input type="number" id="quantity" name="quantity">

  <label for="price">货物单价：</label>
  <input type="text" id="price" name="price">

  <input type="submit" value="提交">
</form>

<?php
if($_SERVER['REQUEST_METHOD'] === 'POST') {
  $quantity = $_POST['quantity'];
  $price = $_POST['price'];

  if($quantity > 0 && $price > 0) {
    $total = $quantity * $price;
    echo "总价为：" . $total;
  } else {
    echo "请输入有效的货物数量和单价";
  }
}
?>

<form action="process.php" method="post">
  <label for="province">选择省份：</label>
  <select id="province" name="province" onchange="updateCities()">
    <option value="浙江省">浙江省</option>
    <option value="江苏省">江苏省</option>
    <option value="广东省">广东省</option>
  </select>

  <label for="city">选择城市：</label>
  <select id="city" name="city">
    <!-- 动态生成的选项 -->
  </select>

  <input type="submit" value="提交">
</form>

<script>
function updateCities() {
  const province = document.getElementById("province").value;
  const citySelect = document.getElementById("city");
  
  citySelect.innerHTML = ""; // 清空之前的选项

  if(province === "浙江省") {
    new Option("杭州市", "杭州市", true, true); // 添加新的选项
    new Option("宁波市", "宁波市");
  } else if(province === "江苏省") {
    new Option("南京市", "南京市", true, true);
    new Option("苏州市", "苏州市");
  } else if(province === "广东省") {
    new Option("广州市", "广州市", true, true);
    new Option("深圳市", "深圳市");
  }
}
</script>

<?php
if($_SERVER['REQUEST_METHOD'] === 'POST') {
  $province = $_POST['province'];
  $city = $_POST['city'];

  echo "您选择的城市是：" . $province . " - " . $city;
}
?>