程序代码：

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

#define STR_LEN 30
#define MAX_LEN 30

int compares_str(void *p, void *q);

main()
    {
    char *p[MAX_LEN], str[STR_LEN+1];
    int n=0, num_p=0, i, j, k;

    for (;;)
        {
        if (num_p>MAX_LEN)
            {
            printf("-- There is no place left --");
            break;
            }
        printf("Enter the sentence: ");
        scanf(" %s",&str);
        if (strcmp(str,"0")==0)
            break;
        while (getchar()!='\n')
            ;
        p[n]=malloc(strlen(str)+1);
        if (p[n]==NULL)
            {
            printf("-- malloc error --");
            break;
            }
        strcpy(p[n++],str);
        num_p++;
        }

    qsort(p,n,STR_LEN+1,compares_str);

    for (i=0;i<n-1;i++)
        {
        for (j=i+1;j<n;j++)
            {
            if (strcmp(p[i],p[j])==0)
                {
                free(p[j]);
                for (k=j;k<n;k++)
                    p[k]=p[k+1];
                }
            }
        }

    for (i=0;i<n;i++)
        printf("%s\n",p[i]);

    getch();
    return 0;
    }

int compares_str(void *p, void *q)
    {
    return strcmp((char *)p,(char *)q);
    }