Make it easy!

#include <SPI.h>
#include <SD.h>
#include <Wire.h>
#include "DS3231.h"

RTClib RTC;
DS3231 Clock;

int Year;
int Month;
int Date;
int Hour;
int Minute;
int Second;
int tempC;
int interval;
int Minute_last;

File myFile;

void setup() {
  Serial.begin(9600);
  Wire.begin(); //for DS3231
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  delay(2000);  //afer reset Arduino, 2s to take out SD

  Serial.print("Initializing SD card...");
  if (!SD.begin(10)) {
    Serial.println("initialization failed!");
  }
  else
  {
    Serial.println("initialization done.");
  }
}

void loop() {
  interval = 1; //interval to write data
  DateTime now = RTC.now();
  Year = now.year();
  Month = now.month();
  Date = now.day();
  Hour = now.hour();
  Minute = now.minute();
  Second = now.second();
  tempC = Clock.getTemperature();
  
  if ((Minute % interval == 0)&(Minute_last!=Minute))
  {
    write_data(tempC);  //write data
    Minute_last = Minute;
  }
}

void write_data(int temperature_input)
{
  myFile = SD.open("test.txt", FILE_WRITE);

  // if the file opened okay, write to it:
  if (myFile) {
    myFile.print(Year);
    myFile.print("/");
    myFile.print(Month);
    myFile.print("/");
    myFile.print(Date);
    myFile.print(" ");
    myFile.print(Hour);
    myFile.print(":");
    myFile.print(Minute);
    myFile.print("_temperature_");
    myFile.println(temperature_input);
    myFile.close();
    Serial.println("Write file successful!"); //print out COM Port
  } else {
    Serial.println("error opening test.txt");
  }
}