Creating a lot of files on an SD Card with an Arduino. Code complies. Keeping it as a reminder of how to work with String to char array conversion

generateFilesOnSDcard.ino

void generateFiles() {
//derived from code found at http://forum.arduino.cc/index.php?topic=57460.0
  String fileName = String();
  String message = String();
  unsigned int filenumber = 1;
  while(!filenumber==0) {
    fileName = "file_";
    fileName += filenumber;
    fileName += ".txt";
    message = fileName;
    char charFileName[fileName.length() + 1];
    fileName.toCharArray(charFileName, sizeof(charFileName));

    if (SD.exists(charFileName)) { 
      message += " exists.";
      filenumber++;
    }
    else {
      File dataFile = SD.open(charFileName, FILE_WRITE);
      message += " created.";
      dataFile.close();
      filenumber = 0;
    }
    Serial.println(message);
  }
}