/* Compares two files, printing the first line where they differ */

#include <stdio.h>

#define MAXLINE 1000

int main(int argc, char *argv[]) {
     char line1[MAXLINE], line2[MAXLINE];
     char *prgname = argv[0];
     FILE *fp1, *fp2;
     int count;

     if (argc != 3) {
	  fprintf(stderr, "%s: error: invalid number of arguments\n", prgname);
	  return 1;
     }
     if ((fp1 = fopen(argv[1], "r")) == NULL) {
	  fprintf(stderr, "%s: error: unable to open file: %s\n", prgname, argv[1]);
	  return 1;
     }
     if ((fp2 = fopen(argv[2], "r")) == NULL) {
	  fprintf(stderr, "%s: error: unable to open file: %s\n", prgname, argv[2]);
	  return 1;
     }

     count = 0;
     while (fgets(line1, MAXLINE, fp1) && fgets(line2, MAXLINE, fp2)) {
	  count++;
	  if (strcmp(line1, line2)) {
	       printf("First difference between files occurs at line %d\n", count);
	       printf("\nFile 1 - %s:\n", argv[1]);
	       printf("%s", line1);
	       printf("\nFile 2 - %s: \n", argv[2]);
	       printf("%s", line2);
	       return 0;
	  }
     }

     if (feof(fp1) && feof(fp2))
	  printf("Files are identical\n");
     else if (feof(fp1))
	  printf("All of %s is identical with the beginning of %s\n", argv[1], argv[2]);
     else if (feof(fp2))
	  printf("All of %s is identical with the beginning of %s\n", argv[2], argv[1]);
     	 
     return 2;
}