Modify the sort program to handle a -r flag, which indicates sorting in reverse (decreasing) order.Be sure that -r works with -n.

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

#define  NUMERIC  1  /*numeric sort     */
#define  DECR     2  /* sort in decreasing order */
#define  LINES    100  /*max # of lines to be sorted */

int  numcmp(char *, char *);
int readlines(char *lineptr[], int maxlines);
void qsort(char *v[], int left, int right,
              int (*comp)(void *, void *));
void writelines(char *lineptr[], int nlines, int decr);

static char option = 0;

/*sort input lines  */
int main(int argc, char *argv[]){
    while(c ==*++argv[0])
      switch(c) {
        case 'n':  /*numeric sort */
              option |= NUMERIC;
              break;
       case 'r':   /* sort in decreasing order */
             option |= DECR;
             break;
      default:
            printf("sort: illegal option %c\n", c);
            argc = 1;
            rc = -1;
            break;
      }
      if(argc)
         printf(:Usage: sort -nr\n");
      else
        if(nlines = readlines(lineptr, LINES)) > 0){
           if(option & NUMERIC)
               qsort((void **) lineptr, 0, nlines- 1,
                     (int (*) (void *, void *)) numcmp);
           else
              qsort((void **) lineptr, 0, nlines -1,
                    (int (*) (void *, void *)) strcmp);
          writelines(lineptr, nlines, option & DECR)
        } else{
             printf("input too big to sort \n");
             rc = -1;
        }
       return rc;
}
/* writelines: write output lines     */
void writelines(char *lineptr[], int nlines, int decr){
     int i;

    if(decr)    /*print in decreasing order */
       for(i =nlines -1; i>= 0; i--)
           printf("%s\n", lineptr[i]);
    else
       for(i = 0; i <nlines; i++)
         printf("%s\n", lineptr[i]);
}