Hex_exchange

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

#define PgUp 0x49
#define PgDn 0x51
#define Up 0x48
#define Dn 0x50

#define Max_PGline 20

void print_hex(char* buf,int *cline,int line,int n,FILE *fp){
   int col;
   n=n>Max_PGline?Max_PGline:n;
   fread(buf, 1, 16*20, fp); // read into memory buffer
   printf("\n\n Hex Dump... \n");
   for(line=0 ; line < n; line++)
   {
     printf("%08x: ",*cline*16);// file position
     for(col=0; col<16; col++)         // 01 01 00 HEX data
       printf("%02X ",buf[line*16+col]);
     for(col=0; col<16; col++)         // ASCII or ....
       if ( isprint(buf[line*16+col]) )   // ctype.h
          printf("%C",buf[line*16+col]);
       else
          printf(".");
     printf("\n");
     *cline=*cline+1;
   }
}

int main(int argc, char *argv[])
{
   char fname[100]; FILE *fp;
   printf("Please enter the file name..:\n");
   scanf("%s", fname);
   if( (fp=fopen(fname,"rb"))== NULL)
   {
       printf("Can't open %s\n", fname);
       system("PAUSE");
       return -1;
   }

   unsigned char hex_buf[20*16];
   int col,c,max_line;
   int current_line = 0,line=0;

   fseek(fp,0,SEEK_END);
   c=ftell(fp);
   max_line=c/16+(c%16!=0?1:0);//get max line
   fseek(fp,0,SEEK_SET);

   printf("PgUp and PgDn \n");
   print_hex(hex_buf,&current_line,line,20,fp);

while(1)
{
   c = getch();  // getch() will return 0 if you press control-function keys
   if(c==27)  break; // ESC
   if (c==224) // PgUp 0x49 or PgDn 0x51
   {
         c = getch();
         if (c == PgUp||c == Up)
         {
               current_line = current_line -(c=(c == PgUp?40:2));
               if (current_line < 0) current_line = 0; //check the line if previous line is out of the file begin
               fseek (fp , current_line*16 , SEEK_SET);
               print_hex(hex_buf,&current_line,line,c-1,fp);
         }
         else if (c == PgDn||c == Dn)
         {
               if(current_line+(c=(c == PgDn?20:1))>max_line) //check the line if next line is out of the file end
                   current_line=max_line-c;
               fseek (fp , current_line*16 , SEEK_SET);
               print_hex(hex_buf,&current_line,line,c,fp);
         }
         else  //another key
         {
               current_line =current_line<Max_PGline?0: current_line - Max_PGline;
               print_hex(hex_buf,&current_line,line,Max_PGline,fp);
         }
    }
    else  //another key
    {
             current_line =current_line<Max_PGline?0: current_line - Max_PGline;
             print_hex(hex_buf,&current_line,line,Max_PGline,fp);
    }
}
  fclose(fp);
  system("PAUSE");
  return 0;
}