Connecting multiple topics- MQTT
just for a closure:

added an array (thank to Juraj):const char* topicsArry[]={deviceTopic, msgTopic, groupTopic, "HomePi/Dvir/Clock", "HomePi/Dvir/Alerts"};

a for loop to over this that loop, and using sizeof ( which was not trivial for me ), led to :

void reconnect() {
        // Loop until we're reconnected
        while (!client.connected()) {
                Serial.print("Attempting MQTT connection...");
                // Attempt to connect
                if (client.connect(deviceName,user, passw)) {
                        Serial.println("connected");
                        pub_msg("Power On");
                        for (int i=0; i&lt;=sizeof(topicsArry)/sizeof(char *); i++){
                          client.subscribe(topicsArry[i]);
                          char msg[50];
                          sprintf(msg, "Subscribed to %s",topicsArry[i]);
                          pub_msg(msg);
                        }
                } else {
                        Serial.print("failed, rc=");
                        Serial.print(client.state());
                        Serial.println(" try again in 5 seconds");
                        // Wait 5 seconds before retrying
                        delay(5000);
                }
        }
}