format string vulnerability exploitation

[nb1]

hello,
I am attempting to exploit a format string vulnerability in a C program in order to 1)crash the program, 2)print out the secret[1] value, 3)modify the secret[1] value, 4) modify the secret[1] value to a pre-determined value. Here is the vulnerable code:

/* vul_prog.c */ 

#define SECRET1 0x44
#define SECRET2 0x55

int main(int argc, char *argv[])
{
  char user_input[100];
  int *secret;
  int int_input;
  int a, b, c, d; /* other variables, not used here.*/

  /* The secret value is stored on the heap */
  secret = (int *) malloc(2*sizeof(int));

  /* getting the secret */
  secret[0] = SECRET1; secret[1] = SECRET2;

  printf("The variable secret's address is 0x%8x (on stack)\n", &secret);
  printf("The variable secret's value is 0x%8x (on heap)\n", secret);
  printf("secret[0]'s address is 0x%8x (on heap)\n", &secret[0]);
  printf("secret[1]'s address is 0x%8x (on heap)\n", &secret[1]);

  printf("Please enter a decimal integer\n");
  scanf("%d", &int_input);  /* getting an input from user */
  printf("Please enter a string\n");
  scanf("%s", user_input); /* getting a string from user */

  /* Vulnerable place */
  printf(user_input);  
  printf("\n");

  /* Verify whether your attack is successful */
  printf("The original secrets: 0x%x -- 0x%x\n", SECRET1, SECRET2);
  printf("The new secrets:      0x%x -- 0x%x\n", secret[0], secret[1]);
  return 0;
}

All I have to do is provide the appropriate input. I've got the first part (how to crash the program), unfortunately I can't figure out any of the other parts. For the second part I tried to provide a series of "%08x" to print out the memory, but I need to print out the actual contents, not the memory addresses. I've been trying to figure this out for days now, any help would be appreciated.
Thanks!!