#include WiFi.h
    #include PubSubClient.h
                        
    const char* ssid = "YourSSID";
    const char* password = "YourPassword";
    const char* mqtt_server = "broker.emqx.io";
                        
    const char* topic = "week13/wifi"; // Topic
                        
    const int switchPin = D2; // Switch Pin
                        
    WiFiClient espClient;
   PubSubClient client(espClient);
                        
    int lastSwitchState = HIGH; // Previous switch state
                        
    void setup() {
                        Serial.begin(115200);
                        pinMode(switchPin, INPUT_PULLUP);
                        setup_wifi();
                        client.setServer(mqtt_server, 1883);
                        }
                        
                        void setup_wifi() {
                        delay(10);
                        Serial.println();
                        Serial.print("Connecting to ");
                        Serial.println(ssid);
                        
                        WiFi.begin(ssid, password);
                        
                        while (WiFi.status() != WL_CONNECTED) {
                        delay(500);
                        Serial.print(".");
                        }
                        
                        Serial.println("");
                        Serial.println("WiFi connected");
                        Serial.println("IP Address: ");
                        Serial.println(WiFi.localIP());
                        }
                        
                        void reconnect() {
                        while (!client.connected()) {
                        Serial.print("Connecting to MQTT server...");
                        if (client.connect("switchClient")) {
                        Serial.println("Connected");
                        } else {
                        Serial.print("failed, rc=");
                        Serial.print(client.state());
                        Serial.println(" trying again in 5 seconds");
                        delay(5000);
                        }
                        }
                        }
                        
             void loop() {
                        if (!client.connected()) {
                        reconnect();
                        }
                        client.loop();
                        
                        int switchState = digitalRead(switchPin);
                        if (switchState != lastSwitchState) { // If there's a change in switch state
                        if (switchState == LOW) {
                        client.publish(topic, "a");
                        Serial.println("Switch pressed");
                        } else {
                        client.publish(topic, "b");
                        Serial.println("Switch released");
                        }
                        lastSwitchState = switchState;
                        }
                        
                        delay(100); // Small delay to avoid switch bounce
                        }