#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <time.h>

#define NOut 10
#define NMax 4000
#define SIZE 256

/* function prototypes */
int compare (const void * a, const void * b); 
int zero_array (long arr[SIZE][SIZE]);
int read_file(long arr[SIZE][SIZE], FILE * fp);
int transfer (long arr[SIZE][SIZE]); 

struct dfreq {
  long int count; // pair frequency
  int code1, code2;
};

/* structure used to store sorted data */
struct dfreq pd[SIZE*SIZE];