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

struct record
{ short int year;
  unsigned char month, day;
  float mint, avgt, maxt;
  float wind;
  short int precip; };

void print_record(struct record * r)
{ printf("%d-%d-%d T=(%.1f, %.1f, %.1f) P=%d W=%.1f\n", 
         r->year, r->month, r->day,
         r->mint, r->avgt, r->maxt,
         r->precip, r->wind); }

int main()
{ FILE * f = fopen("weather.dat", "r");
  if (f == NULL)
  { fprintf(stderr, "Can't read weather.dat\n");
    exit(1); }
  printf("the struct is %d bytes long\n", sizeof(struct record));
  struct record r;

  fseek(f, 0, SEEK_END);
  int flen = ftell(f);
  printf("length of file is %d\n", flen);
  int nrecs = flen / sizeof(r);
  printf("%d records\n", nrecs);

  int wanty, wantm, wantd;
  printf("Enter wanted y m d: ");
  scanf("%d %d %d", & wanty, & wantm, & wantd);

  int minrec = 0, maxrec = nrecs-1;
  while (1)
  { int midrec = (minrec + maxrec) / 2;
    fseek(f, midrec * sizeof(r), SEEK_SET);
    fread(& r, sizeof(r), 1, f);
    if (r.year == wanty && r.month == wantm && r.day == wantd)
    { print_record(& r); 
      break; }
    if (wanty < r.year ||
        wanty == r.year && wantm < r.month ||
        wanty == r.year && wantm == r.month && wantd < r.day)
      maxrec = midrec - 1;
    else
      minrec = midrec + 1; } }