如果用户确实填满了字段，它就不会显示输出

Question

我应该放什么代码以便我的输出＆＃34;你的车费用＆＃34;不会表现出来 我一直想弄清楚要放什么但是失败了。

<?php
// define variables and set to empty values
$costErr = $modelErr = "";
$cost = $model = "";

if ($_SERVER["REQUEST_METHOD"] == "POST") {

  if (empty($_POST["cost"])) {
    $costErr = "Cost is required";
  } else {
    $cost = test_input($_POST["cost"]);
  }

  if (empty($_POST["model"])) {
    $modelErr = "Model is required";
  } else {
    $model = test_input($_POST["model"]);
  }

}
function test_input($data) {
  $data = trim($data);
  $data = stripslashes($data);
  $data = htmlspecialchars($data);
  return $data;
}
?>

当用户在字段上放置内容时输出，但如果用户不想在字段上输入值，则此输出不应显示我该怎么做？

<?php
if (isset($_POST["age"]) && $_POST["age"] === "1 Year" && $_POST["conditon"] === "Yes") { 
  if ($_POST["age"] === "1 Year" && $_POST["conditon"] === "Yes") {
    echo "Your car Costs " .$cost;
    echo "<br>";
    echo "The model of your car is " .$model;
    echo "<br>";
    $price = $cost - ($cost * .20);
    echo "Your car costs in good condition " .$price;
  } else if($_POST["age"] === "1 Year" && $_POST["conditon"] === "No") {
    echo "Your car Costs " .$cost;
    echo "<br>";
    echo "The model of your car is " .$model;
    echo "<br>";
    $price = $cost - ($cost * .20) - ($cost * .10);
    echo "Your car costs in bad condition " .$price;
  }
}
?>