#include <SPI.h>
#include <SD.h>

File myFile;

void setup() 
{

  Serial.begin(9600);

  if (!SD.begin(10)) 
  {
    Serial.println("SD card initialization failed!");
    return;
  }

  myFile = SD.open("test.txt", FILE_WRITE);
  if (myFile) 
  {
    Serial.println("Writing to the file...");
    myFile.println("Hello, world!");
    myFile.close();
  }
  else 
  {
    Serial.println("Error opening the file!");
  }
}

void loop() {}