#include <stdio.h>

int main(void)
{
  FILE *f;
  int r;
  int n;

  f = fopen("data.txt","r");
  if (!f) {
    printf("fopen returned 0. Is there a file named data.txt?\n");
    return 111;
  }

  r = fscanf(f,"%d",&n);

  if (r == 1) {
    printf("fscanf returned 1. The first number in data.txt is %d.\n",n);
    return 0;
  }

  if (r == 0) {
    printf("fscanf returned 0. data.txt starts with something non-numeric.\n");
    return 100;
  }

  printf("fscanf returned -1, ");
  if (ferror(f)) {
    printf("and ferror returned 1. Trouble reading data.txt!\n");
    return 111;
  }
  printf("and ferror returned 0. End of the data.txt file.\n");

  return 0;
}