void swap(void *v[], int i, int j){
     void *temp;

     temp = v[i];
     v[i] = v[j];
      v[j] = temp;
}

#include <stdlib.h>

/*numcmp: compare s1 and s2 numerically */
int numcmp(char *s1, char *s2){
    double v1, v2;

     v1 = atof(s1);
     v2 = atof(s2);
     if (v1 < v2)
         return -1;
     else if (v1 > v2)
          return 1;
     else
          return 0;
}

/*qsort: sort v[left] ... v[right] into increasing order */
void qsort(void *v[], int left, int right,
            int (*comp)(void *, void *)){
     int i, last;
     void swap(void *v[], int ,int);

     if (left >= right)  /*do nothing if array contains */
         return;         /* fewer than two elements */
     swap(v, left, (left + right)/2);
     last = left;
     for (i = left + 1; i<= right;i++)
         if ((*comp)(v[i], v[left]) < 0)
             swap(v, ++last, i);
     swap(v, left, last);
     qsort(v, left, last - 1, comp);
     qsort(v, last + 1, right, comp);
   
}

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

#define MAXLINES  5000  /*max #lines to be sorted */
char *lineptr[MAXLINES];    /*pointers to text lines */

int readlines(char *lineptr[], int nlines);
void writelines(char *lineptr[], int nlines);

void qsort(void *lineptr[], int left, int right, 
           int (*comp)(void *, void *));
int numcmp(char *, char *);

/*sort input lines */
main(int argc, char *argv[]){
     int nlines;   /* number of input lines read */
     int numeric = 0;   /*1 if numeric sort */

      if (argc > 1 && strcmp(argv[1], "-n") == 0)
          numeric = 1;
      if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
         qsort((void **) lineptr, 0, nlines -1,
              (int (*) (void*, void*))(numeric ? numcmp : strcmp));
         writelines(lineptr, nlines);
         return 0;
      }else {
           printf("input too big to sort\n");
           return 1;
       }
}

#include <stdio.h>
#include <string.h>
#define MAXLINE    1000

int getline(char *line, int max);

/*find: print lines that match pattern from 1st arg */
main(int argc, char *argv[]){
    
     char line[MAXLINE];
     long lineno = 0;
     int c, except = 0, number = 0, found = 0;

     while (--argc > 0 && (*++argv[0] == '-')
          while(c == *++argv[0])
               switch(c) {
                case 'x':
                      except = 1;
                      break;
                case 'n':
                      number = 1;
                      break;
                default:
                      printf("find; illegal option %c\n", c);
                      argc = 0;
                      found = -1;
                      break;
               }
       if (argc != 1)
          printf("Usage; find -x -n pattern\n");
       else
          while (getline(line, MAXLINE) > 0){
               lineno++;
               if ((strstr(line, *argv) != NULL) != except){
                  if (number) 
                     printf("%ld: ", lineone);
                  printf("%s", line):
                  found++;
               }
          }
       return found;
 }
/*strstr(s, t) returns a pointer to the first occurrence of the string t in the string s, or NULL if there is none. */

#include <stdio.h>

/*echo command-line arguments; 2nd version */
main(int argc, char *argv[]){
     while (--argc > 0)
           printf((argc > 1) ? "%s" : "%s", *++argv);
     printf("\n");
     return 0;
}

#include <stdio.h>

/*echo command-line arguments; 2nd version */
main(int argc, char *argv[]){
    while(--argc > 0)
         printf("%s%s", *++argv,  (argc > 1) ? " " : "");
    printf("\n");
    return 0;
}

#include <stdio.h>
/*echo command-line arguments:1st version */
main(int argc, char *argv[]){
   int i;
   
 for(i =1; i <argc;i++)
   printf("%s%s", argv[i], (i< argc -1)? " ": "");
 printf("\n");
 return 0;
}

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

#define MAXLINES   5000     /* max #lines to be sorted */

char *lineptr[MAXLINES];      /* pointers to text lines */

int readlines(char *lineptr[], int nlines);
void writelines(char *lineptr[], int nlines);

void qsort(char *lineptr[], int left, int right);

/* sort input lines */
main(){
    int  nlines;      /* number of input lines read */

    if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
        qsort(lineptr, 0, nlines -1);
        writelines(lineptr, nlines);
        return 0;
    } else {
          printf("error: input too big to sort\n");
          return 1;
    }
}

/* strcmp: return <0 if s<t, 0 if s==t, >0 if s>t */
int strcmp(char *s, char *t){
    int i;

    for (i = 0; s[i] == t[i]; i++)
         if (s[i] == '\0')
              return 0;
    return s[i] - t[i];
}
/*strcmp,pointer version: return < 0 if s<t, 0 if s == t, >0 if s>t */
int strcmp(char *s, char *t){
    for (: *s == *t; s++, t++)
         if (*s == '\0')
              return 0;
    return *s - *t;
}