/*
 * filechange.c
 */
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  FILE * fp;
  int count;
  float num;
  long position;

  if( (fp=fopen("numbers", "r+b"))==NULL ) // the + is essential
  {
    printf("filechange can't open file 'numbers' \n");
    exit(1);
  }
  num=0.123456;

  printf("This program replaces the fifth number in the file\n");
  printf("with the number 0.123456.\n");
  if( fseek(fp, 4*(sizeof(float)), 0) !=0 )
  {
    printf("fseek() failed/n");
    exit(1);
  }
  position=ftell(fp);
  
  printf("The current position in the file is \n");
  printf("%d bytes from the beginning.\n", position);

  if( fwrite(&num, sizeof(float), 1, fp) !=1 )
  {
    printf("Write failed!\n");
    exit(1);
  }

  if( fseek(fp, 0,0) != 0 );
  {
    printf("fseek() failed");
    exit(1);
  } 

  num=0.0;
  count=0;
  printf("Number\tData\n");
  while(~eof(fp))
  {
    fread(&num, sizeof(float), 1, fp);
    if(!feof(fp))
    {
      printf("%ld\t%.6f\n", count++, num);
    }
  }
  fclose(fp);

  return 0;
}