Using the Pmod SD with Arduino Uno

/************************************************************************
*
* Test of the Pmod
*
*************************************************************************
* Description: Pmod_SD
* The voltages applied to inputs A0 and A1 are stored in a file
* on the SD card.
*
* Material
* 1. Arduino Uno
* 2. Pmod SD 
* 3. Adafruit module TXB0108
*
************************************************************************/

#define CS 10 // Assignment of the CS pin
#include <SPI.h> // Call of libraries
#include <SD.h>
int tension;

void setup()
{
 Serial.begin(9600); // initialization of serial communication
 Serial.println("Initialisation carte SD");
 pinMode(CS, OUTPUT);
 // Initialisation carte SD
 if (!SD.begin(CS))
 {
  Serial.println(" * Carte absente");
  Serial.println(" * Erreur de cablage");
  return;
 }
 Serial.println("Carte initialisee.");
 delay(2000);
 
}

void loop()
{
 String donnee = ""; // String for storing values to be stored
 for (int i = 0; i < 2; i++) // conversion of voltage and addition to string
 {
  tension = analogRead(i);
  donnee+= String(tension);
  if (i < 1)
  {
   donnee += ","; // add comma between 2 data
  }
 }

 File fichier = SD.open("datalog.txt", FILE_WRITE); // open file datalog.txt
 if (fichier) // if the file is available
 {
  fichier.println(donnee); // write data in file
  fichier.close();
  Serial.println(donnee); // send data in serial monitor
 }
 else // if the file does not exist, display an error
 {
  Serial.println("Erreur d'ouverture fichier");
 }
 delay(1000); // wait 1 sec between metering and recording
}