/************ Module information **************/
int8_t answer;
int onModulePin = 2;
char aux_str[50];

/************ Xively information **************/
char server[ ] = "api.xively.com";
char port[ ] = "8081";
const char pin[] = "0000";
String TCP_message = "0";

/**********************************************************************************************************************/
/**********************************************************************************************************************/
/**********************************                SETUP               ************************************************/
/**********************************************************************************************************************/
/**********************************************************************************************************************/
void setup() {

  pinMode(onModulePin, OUTPUT);
  Serial.begin(115200);
  Serial.println("\n\nStarting...\n\n");


  //Turn on module
  Serial.println("*******************************************************");
  Serial.println("************************* SETUP ***********************");
  Serial.println("******************************************************* \n");
  Serial.println("Turn on the module");
  power_on();
  Serial.println("Module ON \n");

  delay(3000);

  //sets the PIN code
  Serial.println("Sets the PIN code");
  snprintf(aux_str, sizeof(aux_str), "AT+CPIN=%s", pin);
  sendATcommand(aux_str, "OK", 2000);
  Serial.println("PIN code sets \n");

  delay(3000);

  //network registration
  Serial.println("Network registration");
  while ( (sendATcommand("AT+CREG?", "+CREG: 0,1", 500) ||
           sendATcommand("AT+CREG?", "+CREG: 0,5", 500)) == 0 );


  //sets APN, user name and password for the registration
  Serial.println("Authentification to the network");
  sendATcommand("AT+CGSOCKCONT=1,\"mmsbouygtel.com\"", "OK", 2000);
  sendATcommand("AT+CSOCKAUTH=1,1,\"\",\"\"", "OK", 2000);
  Serial.println("Success authentification");
  Serial.println("Success network registration \n");

  Serial.println("*******************************************************");
  Serial.println("********************* SETUP : DONE ********************");
  Serial.println("*******************************************************\n \n");

}

void loop() {

  String coordinates = "2525";
  String distance = "28";
  TCP_message = "{\"method\": \"put\",\"resource\": \"/feeds/1819176350/\",\"params\": {},\"headers\": {\"X-ApiKey\":  \"aLWKMwlAcdlPK9TrLytC1sKrZxWguK2sl0dwHybMFrFTGhvl\"},\"body\": {\"version\": \"1.0.0\",\"datastreams\": [{\"id\": \"Distance\",\"current_value\": \"" + distance + "\"},{\"id\": \"Coordinates\",\"current_value\": \"" + coordinates + "\"}]}}";
  send_data();
}


/**********************************************************************************************************************/
/**********************************************************************************************************************/
/**********************************         SEND DATA TO VIXELY        ************************************************/
/**********************************************************************************************************************/
/**********************************************************************************************************************/

void send_data() {
  char message_TCP [500];
  TCP_message.toCharArray(message_TCP, 500); // converting TCP_message to char inorder for it to pass through AT command

  sprintf(aux_str, "AT+NETOPEN=\"TCP\",%s", port);
  answer = sendATcommand(aux_str, "Network opened", 20000);

  if (answer == 1)
  {
    Serial.println("Network opened");
    sprintf(aux_str, "AT+TCPCONNECT=\"%s\",%s", server, port);
    answer = sendATcommand(aux_str, "Connect ok", 20000);
    if (answer == 1)
    {
      Serial.println("Socket opened");

      sprintf(aux_str, "AT+TCPWRITE=%d", strlen(message_TCP));

      answer = sendATcommand(aux_str, ">", 20000);
      if (answer == 1)
      {
        sendATcommand(message_TCP, "Send OK", 20000);
      }

      sendATcommand("AT+NETCLOSE", "OK", 20000);

    }
    else
    {
      Serial.println("Error opening the socket");
    }
  }
  else
  {
    Serial.println("Error opening the network");
  }

}

/**********************************************************************************************************************/
/**********************************************************************************************************************/
/**********************************            TURN ON MODULE          ************************************************/
/**********************************************************************************************************************/
/**********************************************************************************************************************/

void power_on() {

  uint8_t answer = 0;

  // checks if the module is started
  answer = sendATcommand("AT", "OK", 2000);
  if (answer == 0)
  {
    // power on pulse
    digitalWrite(onModulePin, HIGH);
    delay(3000);
    digitalWrite(onModulePin, LOW);

    // waits for an answer from the module
    while (answer == 0) {
      // Send AT every two seconds and wait for the answer
      answer = sendATcommand("AT", "OK", 5000);
    }
  }
}

/**********************************************************************************************************************/
/**********************************************************************************************************************/
/**********************************        SEND COMMAND       ***********************************************/
/**********************************************************************************************************************/
/**********************************************************************************************************************/

int8_t sendATcommand(char* ATcommand, char* expected_answer1, unsigned int timeout) {

  uint8_t x = 0,  answer = 0;
  char response[100];
  unsigned long previous;

  memset(response, '\0', 100);    // Initialize the string

  delay(100);

  while ( Serial.available() > 0) Serial.read();   // Clean the input buffer

  Serial.println(ATcommand);    // Send the AT command


  x = 0;
  previous = millis();

  // this loop waits for the answer
  do {

    if (Serial.available() != 0) {
      response[x] = Serial.read();
      x++;
      // check if the desired answer is in the response of the module
      if (strstr(response, expected_answer1) != NULL)
      {
        answer = 1;
      }
    }
    // Waits for the asnwer with time out
  } while ((answer == 0) && ((millis() - previous) < timeout));

  return answer;
}

Line 10: error: 'String' does not name a type
compilation terminated due to -Wfatal-errors.