K and R C, Solution to Exercise 7-6:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
Write a C Program to compare two files, printing the first line where they differ.
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#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define MAXLINE 100
/*comp: compare two file, printing the first line where they differ*/
main(int argc, char *argv[])
{
 FILE *fp1, *fp2;
 void filecomp(FILE *fp1, FILE *fp2);
 if(argc != 3){
  fprintf(stderr,"comp:need two file namesn");
  exit(1);
 } else {
  if((fp1 = fopen(*++argv, "r")) == NULL) {
   fprintf(stderr, "comp:can't open %sn",*argv);
   exit(1);
  } else if((fp2 = fopen(*++argv, "r")) == NULL) {
   fprintf(stderr, "comp:can't open %sn",*argv);
   exit(1);
  }else  {
   filecomp(fp1,fp2);
   fclose(fp1);
   fclose(fp2);
   exit(0);

  }
 }
}

//filecomp: compare two files -a line at a time
void filecomp (FILE *fp1, FILE *fp2)
{
 char line1[MAXLINE], line2[MAXLINE];
 char *lp1 = *lp2;
 do{
  lp1 = fgets(line1, MAXLINE, fp1);
  lp2 = fgets(line2, MAXLINE, fp2);
  if(lp1 == line1 && lp2 == line2){

   if(strcmp(line1,line2) !=0) {
    printf("First difference in linen%sn",line1);
    lp1 = lp2 = NULL;
   }
  } else if(lp1 != line1 && lp2 == line2)
   printf("end of first file at linen%sn",line2);
  else if(lp1 == line1 && lp2 == line2)
   printf("end of second file at line n%sn",line1);

 }while(lp1 == line1 && lp2 == line2);
}

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