Datalogger sktech

//SD card attached to SPI bus as follows:
// MOSI - pin 11
// MISO - pin 12
// CLK - pin 13
// CS - pin 4
//

#define DHTPIN 8
#define CSPIN 4
#define SSPIN 10
#define DHTTYPE DHT22

// Date and time functions using a DS1307 RTC connected via I2C and Wire lib
#include "RTClib.h"
#include <DHT.h>
#include <DHT_U.h>
#include <Adafruit_Sensor.h>
#include <SPI.h>
#include <SD.h>

DHT dht(DHTPIN, DHTTYPE);
RTC_DS1307 rtc;
char daysOfTheWeek[7][12] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
File logFile;
bool fileLogged = false;

void setup () {
  while (!Serial); // for Leonardo/Micro/Zero

  dht.begin();
  Serial.begin(9600);

  Serial.println("Initializing RTC...");
  if (! rtc.begin()) {
    Serial.println("Couldn't find RTC");
    return;
  }

  Serial.println("Running RTC...");
  if (! rtc.isrunning()) {
    Serial.println("RTC is NOT running!");
    // following line sets the RTC to the date & time this sketch was compiled
    //rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
    // This line sets the RTC with an explicit date & time, for example to set
    // January 21, 2014 at 3am you would call:
    // rtc.adjust(DateTime(2014, 1, 21, 3, 0, 0));

    return;
  }

  Serial.println("Initializing SD card...");
  // On the Ethernet Shield, CS is pin 4. It's set as an output by default.
  // Note that even if it's not used as the CS pin, the hardware SS pin
  // (10 on most Arduino boards, 53 on the Mega) must be left as an output
  // or the SD library functions will not work.
  pinMode(SSPIN, OUTPUT);

  if (!SD.begin(CSPIN)) { // Initialize the SD card
    Serial.println("SD initialization FAILED!");
    return;
  }
  logFile = SD.open("log.txt", FILE_WRITE); // Open the log.txt file for writing

  if (!logFile) { // If file didn't open successfully
    Serial.println("ERROR opening log.txt on SD card!");
    return;
  }
}

void loop () {
  DateTime now = rtc.now();
  float u = dht.readHumidity();
  float t = dht.readTemperature();

  String  log = String(now.day()) + "/" + String(now.month()) + "/" + String(now.year()) + ";"; // Concat day/month/year
  log += String(now.hour()) + ":" + String(now.minute()) + ":" + String(now.second()) + ";"; // Concat hour/min/sec
  log += String(u) + ";"; // Concat humidity
  log += String(t); // Concat temp

  Serial.println(log); // Print log string to serial

  if (!fileLogged) { // If the log hasn't been written to the SD card yet
    fileLogged = true;
    logFile.println(log); // Write log string to log.txt on SD card
    logFile.close(); // Close the file
  }

  delay(1800000);
}