Write the program tail, which prints the last n lines of its input.By default, n is 10, let us say, but it can be changed by an optional argument, so that tail -n prints the last n lines.The program should behave rationally no matter how unreasonable the input or the value of n.Write the program so that it makes the best use of available storage;lines should be stored as in a sorting program, not in a 2d array of fixed size.

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

#define   DEFLINES   10   /*default # of lines to print */
#define   LINES      100  /* max # of lines to print */
#define   MAXLEN      100 /* max length of an input line */

void error(char *);
int getline(char *, int);

/*print last n lines of the input */
int main(int argc, char *argv[]){
    char *p;
    char *buf;     /*pointer to large buffer */
    char *bufend;    /* end of the buffer */
    char line[MAXLEN];  /*current input line */
    char *lineptr[LINES];   /*pointers to lines read */
    int first, i, last, len, n, nlines;

    if(argc == 1)  /*no argument present   */
       n = DEFLINES;   /* use default # of lines */
    else if (argc == 2 && (*++argv)[0] =='-')
      n = atoi(argv[0] + 1);
    else
       error(" usage: tail [-n]");
    if(n < 1 || n > LINES)   /*unreasoable value for n? */
          n =LINES;
    for(i =0; i <LINES;i++)
       lineptr[i] = NULL;
   if((p=buf=malloc(LINES * MAXLEN)) == NULL)
      error("tail: cannot allocate buf");
   bufend = buf + LINES *MAXLEN;
   last = 0;   /*index of last line read */
   nlines = 0;   /*number of lines read */
   while((len = getline(line, MAXLINE)) > 0){
       if(p + len + 1 >= bufend)
           p = buf;    /* buffer wrap around */
       lineptr[last] = p;
       strcpy(lineptr[last], line)
       if(++last > LINES)
           last = 0;  /* ptrs to buffer wrap around */
       p +=len + 1;
       nlines++;
   }
    if (n > nlines )   /* req. lines more than reqd */
        n = nlines;
    first = last - n;
    if(first < 0)   /* it did wrap around the list */
       first += LINES;
    for(i = first; n--> 0; i=(i + 1) % LINES)
        printf("%s", lineptr[i]);
    return 0;
}
/* error: print error message and exit */
void error(char *s){
     printf("%s\n", s);
     exit(1);
}