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coherent

/*
 * Guess -- like 20 questions.
 *
 * (NOTE: /usr/games/guess should be setuid to `games'.
 *        /usr/games/lib/guess.db should be owned by `games')
 */

#include <stdio.h>

#define	NLINE	128			/* Length of various input buffers */

struct node{
	char *question;
	struct node *yes, *no;	/* if yes==NULL, this is a leaf node */
};
struct node cow = { "a cow", NULL };
struct node *game = { &cow };
char *dbname = "/usr/games/lib/guess.db";
char line[NLINE], question[NLINE];

char *
copy(s)
register char *s;
{
	register char *t, *v;
	int l;
	for(l=0,t=s;*t++;l++);
	v=t=malloc(l+1);
	if(v==NULL){
		printf("Out of space in copy\n");
		leave();
	}
	do;while(*t++ = *s++);
	return(v);
}

char *
freads(f, s)
FILE *f;
register char *s;
{
	register char *v;
	if(fgets(s, NLINE, f)==NULL)
		return(NULL);
	v=s;
	while(*s!='\n' && *s!='\0')
		s++;
	*s='\0';
	return(v);
}
readdb(){
	register c;
	register struct node *p;
	FILE *f;
	int message = 0;
	if((f=fopen(dbname, "r"))==NULL)
		return;
	if(freads(f, line)==NULL){
		fclose(f);
		return;
	}
	game->question=copy(line);
	for(;;){
		p=game;
		while((c=getc(f))=='y' || c=='n'){
			if(p->yes==NULL){
				p->yes=malloc(sizeof(struct node));
				p->no=malloc(sizeof(struct node));
				if(p->yes==NULL || p->no==NULL){
					printf("Out of space in dbread\n");
					exit(1);
				}
				p->yes->question="a corrupt database";
				p->yes->yes=NULL;
				p->no->question="a corrupt database";
				p->no->yes=NULL;
			}
			if(c=='y')
				p=p->yes;
			else
				p=p->no;
		}
		if(c==EOF)
			break;
		if(c!=':' && !message){
			printf("Invalid database\n");
			message++;
		}
		freads(f, line);
		p->question=copy(line);
	}
	fclose(f);
}
writedb(p, f, level)
struct node *p;
FILE *f;
{
	fprintf(f, "%s\n", p->question);
	if(p->yes){
		line[level]='y';
		line[level+1]='\0';
		fprintf(f, "%s:", line);
		writedb(p->yes, f, level+1);
		line[level]='n';
		line[level+1]='\0';
		fprintf(f, "%s:", line);
		writedb(p->no, f, level+1);
	}
}
leave(){
	FILE *f;
	if((f=fopen(dbname, "w"))==NULL){
		printf("Can't create the database\n");
		exit(1);
	}
	writedb(game, f, 0);
	exit(0);
}
main(argc, argv)
char *argv[];
{
	register struct node *p;
	register c;
	if(argc>1)
		dbname=argv[1];
	readdb();
	for(;;){
		printf("Think of something.\n");
		p=game;
		while(p->yes){
			for(;;){
				printf("%s? ", p->question);
				c=answer();
				if(c=='y'){
					p=p->yes;
					break;
				}
				if(c=='n'){
					p=p->no;
					break;
				}
				printf("Answer yes or no.\n");
			}
		}
		for(;;){
			printf("Is %s what you're thinking of? ", p->question);
			c=answer();
			if(c=='y')
				break;
			if(c=='n'){
				printf("I give up.  What are you thinking of? ");
				if(gets(line)==NULL)
					leave();
				printf("What is a yes-or-no answer question to distinguish %s from %s? ", p->question, line);
				if(gets(question)==NULL)
					leave();
				for(;;){
					printf("What is the answer for %s? ", line);
					c=answer();
					if(c=='y' || c=='n')
						break;
					printf("Answer yes or no.\n");
				}
				p->yes=malloc(sizeof(struct node));
				p->no=malloc(sizeof(struct node));
				if(p->yes==NULL || p->no==NULL){
					printf("Out of space\n");
					leave();
				}
				if(c=='y'){
					p->yes->question=copy(line);
					p->no->question=p->question;
				}
				else{
					p->yes->question=p->question;
					p->no->question=copy(line);
				}
				p->question=copy(question);
				p->yes->yes=NULL;
				p->no->yes=NULL;
				break;
			}
			printf("Answer yes or no.\n");
		}
	}
}

answer()
{
	char buf[NLINE];

	if(gets(buf)==NULL)
		leave();
	return(buf[0]);
}

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