回答です

answer/Ex04.php

@@ -0,0 +1,25 @@
+<?php
+// Ex04_answer.php
+
+$dsn = "mysql:host=localhost;dbname=employee_db;charset=utf8";
+$username = "rezouser";
+$password = "Rezo_0000";
+
+try {
+    $pdo = new PDO($dsn, $username, $password);
+    $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
+
+    $salary = isset($_POST['salary']) ? (float)$_POST['salary'] : 1000;
+    $id = isset($_POST['id']) ? (int)$_POST['id'] : 1;
+
+    $stmt = $pdo->prepare("UPDATE employees SET salary = :salary WHERE id = :id");
+    $stmt->bindParam(':salary', $salary, PDO::PARAM_INT);
+    $stmt->bindParam(':id', $id, PDO::PARAM_INT);
+    $stmt->execute();
+
+    echo "更新しました";
+} catch (PDOException $e) {
+    echo "エラー: " . $e->getMessage();
+} finally {
+    $pdo = null;
+}