a. With the standard font, what is the longest message you can write across one line of the display? How many lines can you write?

14 characters message in 6 lines.

a. Include the code that you had to insert to do this in your lab writeup.

#include <SPI.h>

#include <SD.h>

const int chipSelect = 17;

void setup()

{

 // Open serial communications and wait for port to open:

  Serial.begin(9600);

  delay(1000);

  }

  Serial.print("Initializing SD card...");

  pinMode(17, OUTPUT); //set SS pin as output. 

  // see if the card is present and can be initialized:

  if (!SD.begin(chipSelect)) {

    Serial.println("Card failed, or not present");

    // don't do anything more:

    return;

  }

  Serial.println("card initialized.");

  // open the file. note that only one file can be open at a time,

  // so you have to close this one before opening another.

  File dataFile = SD.open("datalog.txt", FILE_WRITE);

  // if the file is available, write to it:

  if (dataFile) {

    dataFile.println("You shall not pass!");

    dataFile.close();

    Serial.println("The file has been modified");

  }  

  // if the file isn't open, pop up an error:

  else {

    Serial.println("error opening datalog.txt");

  } 

 dataFile = SD.open("datalog.txt");

 if (dataFile)

 {

   Serial.println("Modified File: ");

   while(dataFile.available())

   {

     Serial.write(dataFile.read());

   }

   dataFile.close();

 }

 else

   Serial.println("error opening datalog.txt");

}

void loop()

{

}

b. Explain what would you do differently (or show us your code!) to insert the same text string, but at the beginning of the file (without over-writing the current contents).

               use seek and position functions