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+<code C main.cpp>
+#include <Arduino.h>
+#include <WiFi.h>
+#include <MQTT.h>   // 256dpi MQTT library
+//////////////// EDIT THESE ////////////////
+const char* WIFI_SSID     = "YOUR_SSID";
+const char* WIFI_PASSWORD = "YOUR_PASSWORD";
+const char* MQTT_HOST     = "test.mosquitto.org";   // or your lab broker
+const uint16_t MQTT_PORT  = 1883;
+const char* BASE_TOPIC    = "iot/studentname";        // change per student
+////////////////////////////////////////////
+WiFiClient net;
+MQTTClient mqtt(1024);  // 1KB message buffer
+unsigned long lastPub = 0;
+void connectWiFi() {
+  if (WiFi.status() == WL_CONNECTED) return;
+  WiFi.mode(WIFI_STA);
+  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
+  Serial.print("WiFi connecting");
+  while (WiFi.status() != WL_CONNECTED) {
+    delay(500);
+    Serial.print(".");
+  }
+  Serial.printf("\nWiFi OK, IP: %s\n", WiFi.localIP().toString().c_str());
+}
+void messageReceived(String &topic, String &payload) {
+  Serial.printf("Message on %s: %s\n", topic.c_str(), payload.c_str());
+}
+void connectMQTT() {
+  // Build a real String, then pass c_str()
+  String clientId = "esp32-client-" + String((uint32_t)ESP.getEfuseMac(), HEX);
+  Serial.println("MQTT connecting...");
+  while (!mqtt.connect(clientId.c_str())) {
+    Serial.print(".");
+    delay(1000);
+  }
+  Serial.println("\nMQTT connected!");
+  // Optional subscription
+  String subTopic = String(BASE_TOPIC) + "/#";
+  mqtt.subscribe(subTopic);
+  Serial.printf("Subscribed to %s\n", subTopic.c_str());
+}
+void setup() {
+  Serial.begin(115200);
+  delay(500);
+  connectWiFi();
+  mqtt.begin(MQTT_HOST, MQTT_PORT, net);
+  mqtt.onMessage(messageReceived);
+  // Optional: last will so brokers/clients know if we drop
+  String willTopic = String(BASE_TOPIC) + "/status";
+  mqtt.setWill(willTopic.c_str(), "offline", true, 1);
+  connectMQTT();
+  // Publish "online" once connected
+  mqtt.publish(willTopic, "online", true, 1);
+}
+void loop() {
+  connectWiFi();       // ensure WiFi
+  if (!mqtt.connected()) connectMQTT();
+  mqtt.loop();         // non-blocking
+  delay(10);
+  // Publish every 5 seconds
+  if (millis() - lastPub > 5000) {
+    lastPub = millis();
+    String topic = String(BASE_TOPIC) + "/heartbeat";
+    String payload = String("{\"uptime_ms\":") + millis() + "}";
+    bool ok = mqtt.publish(topic, payload);
+    Serial.printf("Publish %s => %s (%s)\n",
+                  topic.c_str(), payload.c_str(), ok ? "OK" : "FAIL");
+  }
+}
+</code>