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<!DOCTYPE html>
<html>
<head>
<title>15. Light and dark</title>
<link rel="stylesheet" href="htpataic.css" type="text/css" />
</head>
<body>
<table class="contents"><tr><td>
<h4>Contents</h4>
<div><a href="htpataic01.html">1. Introduction</a></div>
<div><a href="htpataic02.html">2. The main loop</a></div>
<div><a href="htpataic03.html">3. Locations</a></div>
<div><a href="htpataic04.html">4. Objects</a></div>
<div><a href="htpataic05.html">5. Inventory</a></div>
<div><a href="htpataic06.html">6. Passages</a></div>
<div><a href="htpataic07.html">7. Distance</a></div>
<div><a href="htpataic08.html">8. North, east, south, west</a></div>
<div><a href="htpataic09.html">9. Code generation</a></div>
<div><a href="htpataic10.html">10. More attributes</a></div>
<div><a href="htpataic11.html">11. Conditions</a></div>
<div><a href="htpataic12.html">12. Open and close</a></div>
<div><a href="htpataic13.html">13. The parser</a></div>
<div><a href="htpataic14.html">14. Multiple nouns</a></div>
<div><b>15. Light and dark</b></div>
<div><a href="htpataic16.html">16. Savegame</a></div>
<div><a href="htpataic17.html">17. Test automation</a></div>
<div><a href="htpataic18.html">18. Abbreviations</a></div>
<div><a href="htpataic19.html">19. Conversations</a></div>
<div><a href="htpataic20.html">20. Combat</a></div>
<div><a href="htpataic21.html">21. Multi-player</a></div>
<div><a href="htpataic22.html">22. Client-server</a></div>
<div><a href="htpataic23.html">23. Database</a></div>
<div><a href="htpataic24.html">24. Speech</a></div>
<div><a href="htpataic25.html">25. JavaScript</a></div>
</td></tr></table>
<h1>How to program a text adventure in C</h1>
<p>
by Ruud Helderman
<<a href="mailto:r.helderman@hccnet.nl">r.helderman@hccnet.nl</a>>
</p>
<p>
Licensed under
<a href="https://github.com/helderman/htpataic/blob/master/LICENSE">MIT License</a>
</p>
<h2>15. Light and dark</h2>
<p class="intro">
In many adventures, a lamp is a vital object.
Without it, you cannot make it through the dark caverns that lie ahead.
</p>
<p>
The effect of being in the dark differs from game to game.
Typically, it makes the command ‘look’ ineffective.
In some games (e.g. <a href="https://en.wikipedia.org/wiki/Zork">Zork</a>),
darkness is deadly.
In others, you can still make progress without a light source,
provided you have drawn a detailed map of the dark area.
</p>
<p>
Our game will stay in between;
being in the dark will not get you killed,
but you will not be able to follow any passages either.
An exception will be made for passages that lead back into the light;
it seemed unfair to me to allow the player to run into a dark area,
without an opportunity to get back to where he came from.
</p>
<p>
Alright; so first of all, in darkness you cannot see your surroundings.
</p>
<table class="code"><tr>
<th>location.c</th>
</tr><tr>
<td>
<ol>
<li class="old">#include <stdbool.h></li>
<li class="old">#include <stdio.h></li>
<li class="old">#include "object.h"</li>
<li class="old">#include "misc.h"</li>
<li class="old">#include "match.h"</li>
<li class="old">#include "noun.h"</li>
<li class="old"></li>
<li class="old">bool executeLookAround(void)</li>
<li class="old">{</li>
<li class="new"><span class="old"> </span>if (isLit(player->location))</li>
<li class="new"> {</li>
<li class="old"> printf("You are in %s.\n", player->location->description);</li>
<li class="new"><span class="old"> </span>}</li>
<li class="new"> else</li>
<li class="new"> {</li>
<li class="new"> printf("It is very dark in here.\n");</li>
<li class="new"> }</li>
<li class="old"> listObjectsAtLocation(player->location);</li>
<li class="old"> return true;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">bool executeLook(void)</li>
<li class="old">{</li>
<li class="old"> OBJECT *obj = getVisible("what you want to look at", params[0]);</li>
<li class="old"> switch (getDistance(player, obj))</li>
<li class="old"> {</li>
<li class="old"> case distHereContained:</li>
<li class="old"> printf("Hard to see, try to get it first.\n");</li>
<li class="old"> break;</li>
<li class="old"> case distOverthere:</li>
<li class="old"> printf("Too far away, move closer please.\n");</li>
<li class="old"> break;</li>
<li class="old"> case distNotHere:</li>
<li class="old"> printf("You don't see any %s here.\n", params[0]);</li>
<li class="old"> break;</li>
<li class="old"> case distUnknownObject:</li>
<li class="old"> // already handled by getVisible</li>
<li class="old"> break;</li>
<li class="old"> default:</li>
<li class="old"> printf("%s\n", obj->details);</li>
<li class="old"> listObjectsAtLocation(obj);</li>
<li class="old"> }</li>
<li class="old"> return true;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">static void movePlayer(OBJECT *passage)</li>
<li class="old">{</li>
<li class="old"> printf("%s\n", passage->textGo);</li>
<li class="old"> if (passage->destination != NULL)</li>
<li class="old"> {</li>
<li class="old"> player->location = passage->destination;</li>
<li class="old"> printf("\n");</li>
<li class="old"> executeLookAround();</li>
<li class="old"> }</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">bool executeGo(void)</li>
<li class="old">{</li>
<li class="old"> OBJECT *obj = getVisible("where you want to go", params[0]);</li>
<li class="old"> switch (getDistance(player, obj))</li>
<li class="old"> {</li>
<li class="old"> case distOverthere:</li>
<li class="old"> movePlayer(getPassage(player->location, obj));</li>
<li class="old"> break;</li>
<li class="old"> case distNotHere:</li>
<li class="old"> printf("You don't see any %s here.\n", params[0]);</li>
<li class="old"> break;</li>
<li class="old"> case distUnknownObject:</li>
<li class="old"> // already handled by getVisible</li>
<li class="old"> break;</li>
<li class="old"> default:</li>
<li class="old"> movePlayer(obj);</li>
<li class="old"> }</li>
<li class="old"> return true;</li>
<li class="old">}</li>
</ol>
</td>
</tr></table>
<p>
Secondly, in darkness you cannot see or use nearby objects.
</p>
<table class="code"><tr>
<th>noun.c</th>
</tr><tr>
<td>
<ol>
<li class="old">#include <stdbool.h></li>
<li class="old">#include <stdio.h></li>
<li class="old">#include <string.h></li>
<li class="old">#include "object.h"</li>
<li class="old">#include "misc.h"</li>
<li class="old"></li>
<li class="old">static bool objectHasTag(OBJECT *obj, const char *noun)</li>
<li class="old">{</li>
<li class="old"> if (noun != NULL && *noun != '\0')</li>
<li class="old"> {</li>
<li class="old"> const char **tag;</li>
<li class="old"> for (tag = obj->tags; *tag != NULL; tag++)</li>
<li class="old"> {</li>
<li class="old"> if (strcmp(*tag, noun) == 0) return true;</li>
<li class="old"> }</li>
<li class="old"> }</li>
<li class="old"> return false;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">static OBJECT ambiguousNoun;</li>
<li class="old"></li>
<li class="old">static OBJECT *getObject(const char *noun, OBJECT *from, DISTANCE maxDistance)</li>
<li class="old">{</li>
<li class="old"> OBJECT *obj, *res = NULL;</li>
<li class="old"> for (obj = objs; obj < endOfObjs; obj++)</li>
<li class="old"> {</li>
<li class="old"> if (objectHasTag(obj, noun) && getDistance(from, obj) <= maxDistance)</li>
<li class="old"> {</li>
<li class="old"> res = res == NULL ? obj : &ambiguousNoun;</li>
<li class="old"> }</li>
<li class="old"> }</li>
<li class="old"> return res;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">OBJECT *getVisible(const char *intention, const char *noun)</li>
<li class="old">{</li>
<li class="old"> OBJECT *obj = getObject(noun, player, distOverthere);</li>
<li class="old"> if (obj == NULL)</li>
<li class="old"> {</li>
<li class="old"> if (getObject(noun, player, distNotHere) == NULL)</li>
<li class="old"> {</li>
<li class="old"> printf("I don't understand %s.\n", intention);</li>
<li class="old"> }</li>
<li class="new"><span class="old"> else </span>if (isLit(player->location))</li>
<li class="old"> {</li>
<li class="old"> printf("You don't see any %s here.\n", noun);</li>
<li class="new"><span class="old"> </span>}</li>
<li class="new"> else</li>
<li class="new"> {</li>
<li class="new"> printf("It's too dark.\n");</li>
<li class="old"> }</li>
<li class="old"> }</li>
<li class="old"> else if (obj == &ambiguousNoun)</li>
<li class="old"> {</li>
<li class="old"> printf("Please be specific about which %s you mean.\n", noun);</li>
<li class="old"> obj = NULL;</li>
<li class="old"> }</li>
<li class="old"> return obj;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">OBJECT *getPossession(OBJECT *from, const char *verb, const char *noun)</li>
<li class="old">{</li>
<li class="old"> OBJECT *obj = NULL;</li>
<li class="old"> if (from == NULL)</li>
<li class="old"> {</li>
<li class="old"> printf("I don't understand who you want to %s.\n", verb);</li>
<li class="old"> }</li>
<li class="old"> else if ((obj = getObject(noun, from, distHeldContained)) == NULL)</li>
<li class="old"> {</li>
<li class="old"> if (getObject(noun, player, distNotHere) == NULL)</li>
<li class="old"> {</li>
<li class="old"> printf("I don't understand what you want to %s.\n", verb);</li>
<li class="old"> }</li>
<li class="old"> else if (from == player)</li>
<li class="old"> {</li>
<li class="old"> printf("You are not holding any %s.\n", noun);</li>
<li class="old"> }</li>
<li class="old"> else</li>
<li class="old"> {</li>
<li class="old"> printf("There appears to be no %s you can get from %s.\n",</li>
<li class="old"> noun, from->description);</li>
<li class="old"> }</li>
<li class="old"> }</li>
<li class="old"> else if (obj == &ambiguousNoun)</li>
<li class="old"> {</li>
<li class="old"> printf("Please be specific about which %s you want to %s.\n",</li>
<li class="old"> noun, verb);</li>
<li class="old"> obj = NULL;</li>
<li class="old"> }</li>
<li class="old"> else if (obj == from)</li>
<li class="old"> {</li>
<li class="old"> printf("You should not be doing that to %s.\n", obj->description);</li>
<li class="old"> obj = NULL;</li>
<li class="old"> }</li>
<li class="old"> return obj;</li>
<li class="old">}</li>
</ol>
</td>
</tr></table>
<p>
In both cases, we used a function <i>isLit</i>.
It is defined (and used some more) in <i>misc.c</i>.
</p>
<table class="code"><tr>
<th>misc.h</th>
</tr><tr>
<td>
<ol>
<li class="old">typedef enum {</li>
<li class="old"> distSelf,</li>
<li class="old"> distHeld,</li>
<li class="old"> distHeldContained,</li>
<li class="old"> distLocation,</li>
<li class="old"> distHere,</li>
<li class="old"> distHereContained,</li>
<li class="old"> distOverthere,</li>
<li class="old"> distNotHere,</li>
<li class="old"> distUnknownObject</li>
<li class="old">} DISTANCE;</li>
<li class="old"></li>
<li class="old">extern bool isHolding(OBJECT *container, OBJECT *obj);</li>
<li class="new">extern bool isLit(OBJECT *location);</li>
<li class="old">extern OBJECT *getPassage(OBJECT *from, OBJECT *to);</li>
<li class="old">extern DISTANCE getDistance(OBJECT *from, OBJECT *to);</li>
<li class="old">extern OBJECT *actorHere(void);</li>
<li class="old">extern int listObjectsAtLocation(OBJECT *location);</li>
</ol>
</td>
</tr><tr>
<th>misc.c</th>
</tr><tr>
<td>
<ol>
<li class="old">#include <stdbool.h></li>
<li class="old">#include <stdio.h></li>
<li class="old">#include "object.h"</li>
<li class="old">#include "misc.h"</li>
<li class="old"></li>
<li class="old">bool isHolding(OBJECT *container, OBJECT *obj)</li>
<li class="old">{</li>
<li class="old"> return validObject(obj) && obj->location == container;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="new">bool isLit(OBJECT *target)</li>
<li class="new">{</li>
<li class="new"> OBJECT *obj;</li>
<li class="new"> if (validObject(target))</li>
<li class="new"> {</li>
<li class="new"> if (target->light > 0)</li>
<li class="new"> {</li>
<li class="new"> return true;</li>
<li class="new"> }</li>
<li class="new"> for (obj = objs; obj < endOfObjs; obj++)</li>
<li class="new"> {</li>
<li class="new"> if (validObject(obj) && obj->light > 0 &&</li>
<li class="new"> (isHolding(target, obj) || isHolding(target, obj->location)))</li>
<li class="new"> {</li>
<li class="new"> return true;</li>
<li class="new"> }</li>
<li class="new"> }</li>
<li class="new"> }</li>
<li class="new"> return false;</li>
<li class="new">}</li>
<li class="new"></li>
<li class="new">static bool isNoticeable(OBJECT *obj)</li>
<li class="new">{</li>
<li class="new"> return obj->location == player ||</li>
<li class="new"> isLit(obj) || isLit(obj->prospect) || isLit(player->location);</li>
<li class="new">}</li>
<li class="old"></li>
<li class="old">OBJECT *getPassage(OBJECT *from, OBJECT *to)</li>
<li class="old">{</li>
<li class="old"> if (from != NULL && to != NULL)</li>
<li class="old"> {</li>
<li class="old"> OBJECT *obj;</li>
<li class="old"> for (obj = objs; obj < endOfObjs; obj++)</li>
<li class="old"> {</li>
<li class="old"> if (isHolding(from, obj) && obj->prospect == to)</li>
<li class="old"> {</li>
<li class="old"> return obj;</li>
<li class="old"> }</li>
<li class="old"> }</li>
<li class="old"> }</li>
<li class="old"> return NULL;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">DISTANCE getDistance(OBJECT *from, OBJECT *to)</li>
<li class="old">{</li>
<li class="old"> return to == NULL ? distUnknownObject :</li>
<li class="old"> !validObject(to) ? distNotHere :</li>
<li class="old"> to == from ? distSelf :</li>
<li class="old"> isHolding(from, to) ? distHeld :</li>
<li class="new"><span class="old"> </span>!isNoticeable(to) ? distNotHere :</li>
<li class="old"> isHolding(to, from) ? distLocation :</li>
<li class="old"> isHolding(from->location, to) ? distHere :</li>
<li class="old"> isHolding(from, to->location) ? distHeldContained :</li>
<li class="old"> isHolding(from->location, to->location) ? distHereContained :</li>
<li class="old"> getPassage(from->location, to) != NULL ? distOverthere :</li>
<li class="old"> distNotHere;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">OBJECT *actorHere(void)</li>
<li class="old">{</li>
<li class="old"> OBJECT *obj;</li>
<li class="old"> for (obj = objs; obj < endOfObjs; obj++)</li>
<li class="old"> {</li>
<li class="old"> if (isHolding(player->location, obj) && obj != player &&</li>
<li class="new"><span class="old"> </span>isNoticeable(obj) &&<span class="old"> obj->health > 0)</span></li>
<li class="old"> {</li>
<li class="old"> return obj;</li>
<li class="old"> }</li>
<li class="old"> }</li>
<li class="old"> return NULL;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">int listObjectsAtLocation(OBJECT *location)</li>
<li class="old">{</li>
<li class="old"> int count = 0;</li>
<li class="old"> OBJECT *obj;</li>
<li class="old"> for (obj = objs; obj < endOfObjs; obj++)</li>
<li class="old"> {</li>
<li class="new"><span class="old"> if (obj != player && isHolding(location, </span>obj) && isNoticeable(obj))</li>
<li class="old"> {</li>
<li class="old"> if (count++ == 0)</li>
<li class="old"> {</li>
<li class="old"> printf("%s:\n", location->contents);</li>
<li class="old"> }</li>
<li class="old"> printf("%s\n", obj->description);</li>
<li class="old"> }</li>
<li class="old"> }</li>
<li class="old"> return count;</li>
<li class="old">}</li>
</ol>
</td>
</tr></table>
<div class="explanation">
<p>
Explanation:
</p>
<ul>
<li>Line 11-30:
<i>isLit</i> will be used to check if a given location is light or dark.
Note: it is not enough to simply check attribute <i>light</i> of the location;
the location could be lit by a lamp.
</li>
<li>Line 32-36:
<i>isNoticeable</i> takes it one step further;
it works for every object, not just locations and lamps.
It also takes into account that objects in the player’s inventory
can always be used, even in the dark.
</li>
<li>Line 60:
nearby objects that remain hidden in the dark,
are being treated as ‘not here’.
This naturally prevents the game from leaking information
about objects the player is not supposed to be aware of.
</li>
</ul>
</div>
<p>
The implementation of <i>isLit</i> uses a new attribute <i>light</i>.
</p>
<table class="code"><tr>
<th>object.awk</th>
</tr><tr>
<td>
<ol>
<li class="old">BEGIN {</li>
<li class="old"> count = 0;</li>
<li class="old"> obj = "";</li>
<li class="old"> if (pass == "c2") {</li>
<li class="old"> print "\nstatic bool alwaysTrue(void) { return true; }";</li>
<li class="old"> print "\nOBJECT objs[] = {";</li>
<li class="old"> }</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">/^- / {</li>
<li class="old"> outputRecord(",");</li>
<li class="old"> obj = $2;</li>
<li class="old"> prop["condition"] = "alwaysTrue";</li>
<li class="old"> prop["description"] = "NULL";</li>
<li class="old"> prop["tags"] = "";</li>
<li class="old"> prop["location"] = "NULL";</li>
<li class="old"> prop["destination"] = "NULL";</li>
<li class="old"> prop["prospect"] = "";</li>
<li class="old"> prop["details"] = "\"You see nothing special.\"";</li>
<li class="old"> prop["contents"] = "\"You see\"";</li>
<li class="old"> prop["textGo"] = "\"You can't get much closer than this.\"";</li>
<li class="old"> prop["weight"] = "99";</li>
<li class="old"> prop["capacity"] = "0";</li>
<li class="old"> prop["health"] = "0";</li>
<li class="new"> prop["light"] = "0";</li>
<li class="old"> prop["open"] = "cannotBeOpened";</li>
<li class="old"> prop["close"] = "cannotBeClosed";</li>
<li class="old"> prop["lock"] = "cannotBeLocked";</li>
<li class="old"> prop["unlock"] = "cannotBeUnlocked";</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">obj && /^[ \t]+[a-z]/ {</li>
<li class="old"> name = $1;</li>
<li class="old"> $1 = "";</li>
<li class="old"> if (name in prop) {</li>
<li class="old"> prop[name] = $0;</li>
<li class="old"> if (/^[ \t]*\{/) {</li>
<li class="old"> prop[name] = name count;</li>
<li class="old"> if (pass == "c1") print "static bool " prop[name] "(void) " $0;</li>
<li class="old"> }</li>
<li class="old"> }</li>
<li class="old"> else if (pass == "c2") {</li>
<li class="old"> print "#error \"" FILENAME " line " NR ": unknown attribute '" name "'\"";</li>
<li class="old"> }</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">!obj && pass == (/^#include/ ? "c1" : "h") {</li>
<li class="old"> print;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">END {</li>
<li class="old"> outputRecord("\n};");</li>
<li class="old"> if (pass == "h") {</li>
<li class="old"> print "\n#define endOfObjs\t(objs + " count ")";</li>
<li class="old"> print "\n#define validObject(obj)\t" \</li>
<li class="old"> "((obj) != NULL && (*(obj)->condition)())";</li>
<li class="old"> }</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">function outputRecord(separator)</li>
<li class="old">{</li>
<li class="old"> if (obj) {</li>
<li class="old"> if (pass == "h") {</li>
<li class="old"> print "#define " obj "\t(objs + " count ")";</li>
<li class="old"> }</li>
<li class="old"> else if (pass == "c1") {</li>
<li class="old"> print "static const char *tags" count "[] = {" prop["tags"] ", NULL};";</li>
<li class="old"> }</li>
<li class="old"> else if (pass == "c2") {</li>
<li class="old"> print "\t{\t/* " count " = " obj " */";</li>
<li class="old"> print "\t\t" prop["condition"] ",";</li>
<li class="old"> print "\t\t" prop["description"] ",";</li>
<li class="old"> print "\t\ttags" count ",";</li>
<li class="old"> print "\t\t" prop["location"] ",";</li>
<li class="old"> print "\t\t" prop["destination"] ",";</li>
<li class="old"> print "\t\t" prop[prop["prospect"] ? "prospect" : "destination"] ",";</li>
<li class="old"> print "\t\t" prop["details"] ",";</li>
<li class="old"> print "\t\t" prop["contents"] ",";</li>
<li class="old"> print "\t\t" prop["textGo"] ",";</li>
<li class="old"> print "\t\t" prop["weight"] ",";</li>
<li class="old"> print "\t\t" prop["capacity"] ",";</li>
<li class="old"> print "\t\t" prop["health"] ",";</li>
<li class="new"> print "\t\t" prop["light"] ",";</li>
<li class="old"> print "\t\t" prop["open"] ",";</li>
<li class="old"> print "\t\t" prop["close"] ",";</li>
<li class="old"> print "\t\t" prop["lock"] ",";</li>
<li class="old"> print "\t\t" prop["unlock"];</li>
<li class="old"> print "\t}" separator;</li>
<li class="old"> delete prop;</li>
<li class="old"> }</li>
<li class="old"> count++;</li>
<li class="old"> }</li>
<li class="old">}</li>
</ol>
</td>
</tr></table>
<p>
By default, <i>light</i> is zero, meaning an object does not emit light.
Every location in broad daylight (typically all but the underground ones)
will be given a positive <i>light</i> value.
It doesn’t really matter what value that is; as long as it’s not zero.
We will also add a lamp the player can carry to traverse dark areas.
</p>
<table class="code"><tr>
<th>object.txt</th>
</tr><tr>
<td>
<ol>
<li class="old">#include <stdbool.h></li>
<li class="old">#include <stdio.h></li>
<li class="old">#include "object.h"</li>
<li class="old">#include "toggle.h"</li>
<li class="old"></li>
<li class="old">typedef struct object {</li>
<li class="old"> bool (*condition)(void);</li>
<li class="old"> const char *description;</li>
<li class="old"> const char **tags;</li>
<li class="old"> struct object *location;</li>
<li class="old"> struct object *destination;</li>
<li class="old"> struct object *prospect;</li>
<li class="old"> const char *details;</li>
<li class="old"> const char *contents;</li>
<li class="old"> const char *textGo;</li>
<li class="old"> int weight;</li>
<li class="old"> int capacity;</li>
<li class="old"> int health;</li>
<li class="new"> int light;</li>
<li class="old"> void (*open)(void);</li>
<li class="old"> void (*close)(void);</li>
<li class="old"> void (*lock)(void);</li>
<li class="old"> void (*unlock)(void);</li>
<li class="old">} OBJECT;</li>
<li class="old"></li>
<li class="old">extern OBJECT objs[];</li>
<li class="old"></li>
<li class="old">- field</li>
<li class="old"> description "an open field"</li>
<li class="old"> tags "field"</li>
<li class="old"> details "The field is a nice and quiet place under a clear blue sky."</li>
<li class="old"> capacity 9999</li>
<li class="new"> light 100</li>
<li class="old"></li>
<li class="old">- cave</li>
<li class="old"> description "a little cave"</li>
<li class="old"> tags "cave"</li>
<li class="old"> details "The cave is just a cold, damp, rocky chamber."</li>
<li class="old"> capacity 9999</li>
<li class="old"></li>
<li class="old">- silver</li>
<li class="old"> description "a silver coin"</li>
<li class="old"> tags "silver", "coin", "silver coin"</li>
<li class="old"> location field</li>
<li class="old"> details "The coin has an eagle on the obverse."</li>
<li class="old"> weight 1</li>
<li class="old"></li>
<li class="old">- gold</li>
<li class="old"> description "a gold coin"</li>
<li class="old"> tags "gold", "coin", "gold coin"</li>
<li class="old"> location openBox</li>
<li class="old"> details "The shiny coin seems to be a rare and priceless artefact."</li>
<li class="old"> weight 1</li>
<li class="old"></li>
<li class="old">- guard</li>
<li class="old"> description "a burly guard"</li>
<li class="old"> tags "guard", "burly guard"</li>
<li class="old"> location field</li>
<li class="old"> details "The guard is a really big fellow."</li>
<li class="old"> contents "He has"</li>
<li class="old"> health 100</li>
<li class="old"> capacity 20</li>
<li class="old"></li>
<li class="old">- player</li>
<li class="old"> description "yourself"</li>
<li class="old"> tags "yourself"</li>
<li class="old"> location field</li>
<li class="old"> details "You would need a mirror to look at yourself."</li>
<li class="old"> contents "You have"</li>
<li class="old"> health 100</li>
<li class="old"> capacity 20</li>
<li class="old"></li>
<li class="old">- intoCave</li>
<li class="old"> condition { return guard->health == 0 || silver->location == guard; }</li>
<li class="old"> description "a cave entrance to the east"</li>
<li class="old"> tags "east", "entrance"</li>
<li class="old"> location field</li>
<li class="old"> destination cave</li>
<li class="old"> details "The entrance is just a narrow opening in a small outcrop."</li>
<li class="old"> textGo "You walk into the cave."</li>
<li class="old"> open isAlreadyOpen</li>
<li class="old"></li>
<li class="old">- intoCaveBlocked</li>
<li class="old"> condition { return guard->health > 0 && silver->location != guard; }</li>
<li class="old"> description "a cave entrance to the east"</li>
<li class="old"> tags "east", "entrance"</li>
<li class="old"> location field</li>
<li class="old"> prospect cave</li>
<li class="old"> details "The entrance is just a narrow opening in a small outcrop."</li>
<li class="old"> textGo "The guard stops you from walking into the cave."</li>
<li class="old"> open isAlreadyOpen</li>
<li class="old"></li>
<li class="old">- exitCave</li>
<li class="old"> description "an exit to the west"</li>
<li class="old"> tags "west", "exit"</li>
<li class="old"> location cave</li>
<li class="old"> destination field</li>
<li class="old"> details "Sunlight pours in through an opening in the cave's wall."</li>
<li class="old"> textGo "You walk out of the cave."</li>
<li class="old"> open isAlreadyOpen</li>
<li class="old"></li>
<li class="old">- wallField</li>
<li class="old"> description "dense forest all around"</li>
<li class="old"> tags "west", "north", "south", "forest"</li>
<li class="old"> location field</li>
<li class="old"> details "The field is surrounded by trees and undergrowth."</li>
<li class="old"> textGo "Dense forest is blocking the way."</li>
<li class="old"></li>
<li class="old">- wallCave</li>
<li class="old"> description "solid rock all around"</li>
<li class="old"> tags "east", "north", "rock"</li>
<li class="old"> location cave</li>
<li class="old"> details "Carved in stone is a secret password 'abccb'."</li>
<li class="old"> textGo "Solid rock is blocking the way."</li>
<li class="old"></li>
<li class="old">- backroom</li>
<li class="old"> description "a backroom"</li>
<li class="old"> tags "backroom"</li>
<li class="old"> details "The room is dusty and messy."</li>
<li class="old"> capacity 9999</li>
<li class="old"></li>
<li class="old">- wallBackroom</li>
<li class="old"> description "solid rock all around"</li>
<li class="old"> tags "east", "west", "south", "rock"</li>
<li class="old"> location backroom</li>
<li class="old"> details "Trendy wallpaper covers the rock walls."</li>
<li class="old"> textGo "Solid rock is blocking the way."</li>
<li class="old"></li>
<li class="old">- openDoorToBackroom</li>
<li class="old"> description "an open door to the south"</li>
<li class="old"> tags "south", "door", "doorway"</li>
<li class="old"> destination backroom</li>
<li class="old"> details "The door is open."</li>
<li class="old"> textGo "You walk through the door into a backroom."</li>
<li class="old"> open isAlreadyOpen</li>
<li class="old"> close toggleDoorToBackroom</li>
<li class="old"></li>
<li class="old">- closedDoorToBackroom</li>
<li class="old"> description "a closed door to the south"</li>
<li class="old"> tags "south", "door", "doorway"</li>
<li class="old"> location cave</li>
<li class="old"> prospect backroom</li>
<li class="old"> details "The door is closed."</li>
<li class="old"> textGo "The door is closed."</li>
<li class="old"> open toggleDoorToBackroom</li>
<li class="old"> close isAlreadyClosed</li>
<li class="old"></li>
<li class="old">- openDoorToCave</li>
<li class="old"> description "an open door to the north"</li>
<li class="old"> tags "north", "door", "doorway"</li>
<li class="old"> destination cave</li>
<li class="old"> details "The door is open."</li>
<li class="old"> textGo "You walk through the door into the cave."</li>
<li class="old"> open isAlreadyOpen</li>
<li class="old"> close toggleDoorToCave</li>
<li class="old"></li>
<li class="old">- closedDoorToCave</li>
<li class="old"> description "a closed door to the north"</li>
<li class="old"> tags "north", "door", "doorway"</li>
<li class="old"> location backroom</li>
<li class="old"> prospect cave</li>
<li class="old"> details "The door is closed."</li>
<li class="old"> textGo "The door is closed."</li>
<li class="old"> open toggleDoorToCave</li>
<li class="old"> close isAlreadyClosed</li>
<li class="old"></li>
<li class="old">- openBox</li>
<li class="old"> description "a wooden box"</li>
<li class="old"> tags "box", "wooden box"</li>
<li class="old"> details "The box is open."</li>
<li class="old"> weight 5</li>
<li class="old"> capacity 10</li>
<li class="old"> open isAlreadyOpen</li>
<li class="old"> close toggleBox</li>
<li class="old"> lock isStillOpen</li>
<li class="old"> unlock isAlreadyOpen</li>
<li class="old"></li>
<li class="old">- closedBox</li>
<li class="old"> description "a wooden box"</li>
<li class="old"> tags "box", "wooden box"</li>
<li class="old"> details "The box is closed."</li>
<li class="old"> weight 5</li>
<li class="old"> open toggleBox</li>
<li class="old"> close isAlreadyClosed</li>
<li class="old"> lock toggleBoxLock</li>
<li class="old"> unlock isAlreadyUnlocked</li>
<li class="old"></li>
<li class="old">- lockedBox</li>
<li class="old"> description "a wooden box"</li>
<li class="old"> tags "box", "wooden box"</li>
<li class="old"> location backroom</li>
<li class="old"> details "The box is closed."</li>
<li class="old"> weight 5</li>
<li class="old"> open isStillLocked</li>
<li class="old"> close isAlreadyClosed</li>
<li class="old"> lock isAlreadyLocked</li>
<li class="old"> unlock toggleBoxLock</li>
<li class="old"></li>
<li class="old">- keyForBox</li>
<li class="old"> description "a tiny key"</li>
<li class="old"> tags "key", "tiny key"</li>
<li class="old"> location cave</li>
<li class="old"> details "The key is really small and shiny."</li>
<li class="old"> weight 1</li>
<li class="new"></li>
<li class="new">- lampOff</li>
<li class="new"> description "a lamp"</li>
<li class="new"> tags "lamp"</li>
<li class="new"> location field</li>
<li class="new"> details "The lamp is off."</li>
<li class="new"> weight 5</li>
<li class="new"></li>
<li class="new">- lampOn</li>
<li class="new"> description "a lamp"</li>
<li class="new"> tags "lamp"</li>
<li class="new"> details "The lamp is on."</li>
<li class="new"> weight 5</li>
<li class="new"> light 100</li>
</ol>
</td>
</tr></table>
<div class="explanation">
<p>
Explanation:
</p>
<ul>
<li>Line 19:
the new attribute.
</li>
<li>Line 33:
so far, the field is the only location with ‘natural’ light.
</li>
<li>Line 206-218:
for the lamp we actually have two objects:
the lamp being off and the lamp being on.
But the player will only get to see one at a time;
together they act as a single item.
</li>
</ul>
</div>
<p>
We will add some commands we can use to turn the lamp on and off.
</p>
<table class="code"><tr>
<th>parsexec.c</th>
</tr><tr>
<td>
<ol>
<li class="old">#include <ctype.h></li>
<li class="old">#include <stdbool.h></li>
<li class="old">#include <stdio.h></li>
<li class="old">#include "object.h"</li>
<li class="old">#include "misc.h"</li>
<li class="old">#include "match.h"</li>
<li class="old">#include "location.h"</li>
<li class="old">#include "inventory.h"</li>
<li class="old">#include "inventory2.h"</li>
<li class="old">#include "openclose.h"</li>
<li class="new">#include "onoff.h"</li>
<li class="old"></li>
<li class="old">typedef struct</li>
<li class="old">{</li>
<li class="old"> const char *pattern;</li>
<li class="old"> bool (*function)(void);</li>
<li class="old">} COMMAND;</li>
<li class="old"></li>
<li class="old">static bool executeQuit(void)</li>
<li class="old">{</li>
<li class="old"> return false;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">static bool executeNoMatch(void)</li>
<li class="old">{</li>
<li class="old"> const char *src = *params;</li>
<li class="old"> int len;</li>
<li class="old"> for (len = 0; src[len] != '\0' && !isspace(src[len]); len++);</li>
<li class="old"> if (len > 0) printf("I don't know how to '%.*s'.\n", len, src);</li>
<li class="old"> return true;</li>
<li class="old">}</li>
<li class="old"></li>
<li class="old">bool parseAndExecute(const char *input)</li>
<li class="old">{</li>
<li class="old"> static const COMMAND commands[] =</li>
<li class="old"> {</li>
<li class="old"> { "quit" , executeQuit },</li>
<li class="old"> { "look" , executeLookAround },</li>
<li class="old"> { "look around" , executeLookAround },</li>
<li class="old"> { "look at A" , executeLook },</li>
<li class="old"> { "look A" , executeLook },</li>
<li class="old"> { "examine A" , executeLook },</li>
<li class="old"> { "go to A" , executeGo },</li>
<li class="old"> { "go A" , executeGo },</li>
<li class="old"> { "get A from B" , executeGetFrom },</li>
<li class="old"> { "get A" , executeGet },</li>
<li class="old"> { "put A in B" , executePutIn },</li>
<li class="old"> { "drop A in B" , executePutIn },</li>
<li class="old"> { "drop A" , executeDrop },</li>
<li class="old"> { "ask A from B" , executeAskFrom },</li>
<li class="old"> { "ask A" , executeAsk },</li>
<li class="old"> { "give A to B" , executeGiveTo },</li>
<li class="old"> { "give A" , executeGive },</li>
<li class="old"> { "inventory" , executeInventory },</li>
<li class="old"> { "open A" , executeOpen },</li>
<li class="old"> { "close A" , executeClose },</li>
<li class="old"> { "lock A" , executeLock },</li>
<li class="old"> { "unlock A" , executeUnlock },</li>
<li class="new"> { "turn on A" , executeTurnOn },</li>
<li class="new"> { "turn off A" , executeTurnOff },</li>
<li class="new"> { "turn A on" , executeTurnOn },</li>
<li class="new"> { "turn A off" , executeTurnOff },</li>
<li class="old"> { "A" , executeNoMatch }</li>
<li class="old"> };</li>
<li class="old"> const COMMAND *cmd;</li>
<li class="old"> for (cmd = commands; !matchCommand(input, cmd->pattern); cmd++);</li>
<li class="old"> return (*cmd->function)();</li>
<li class="old">}</li>
</ol>
</td>
</tr></table>
<p>
Below is the implementation of these commands.
</p>
<table class="demo">
<tr><th>Sample output</th></tr>
<tr><td>
Welcome to Little Cave Adventure.<br />
You are in an open field.<br />
You see:<br />
a silver coin<br />
a burly guard<br />
a cave entrance to the east<br />
dense forest all around<br />
a lamp<br />
<br />
--> get lamp<br />
You pick up a lamp.<br />
<br />
--> get coin<br />
You pick up a silver coin.<br />
<br />
--> give coin<br />
You give a silver coin to a burly guard.<br />
<br />
--> go cave<br />
You walk into the cave.<br />
<br />
It is very dark in here.<br />
You see:<br />
an exit to the west<br />
<br />
--> get key<br />
It's too dark.<br />
<br />
--> open door<br />
It's too dark.<br />
<br />
--> go south<br />
It's too dark.<br />
<br />
--> turn lamp on<br />
You turn on a lamp.<br />
<br />
You are in a little cave.<br />
You see:<br />
an exit to the west<br />
solid rock all around<br />
a closed door to the south<br />
a tiny key<br />
<br />
--> look around<br />
You are in a little cave.<br />
You see:<br />
an exit to the west<br />
solid rock all around<br />
a closed door to the south<br />
a tiny key<br />
<br />
--> get key<br />
You pick up a tiny key.<br />
<br />
--> open door<br />
You open a closed door to the south.<br />
<br />
--> go south<br />
You walk through the door into a backroom.<br />
<br />
You are in a backroom.<br />
You see:<br />
solid rock all around<br />
an open door to the north<br />
a wooden box<br />
<br />
--> quit<br />
<br />
Bye!<br />
</td></tr>
</table>
<table class="code"><tr>
<th>onoff.h</th>
</tr><tr>
<td>
<ol>
<li class="new">extern bool executeTurnOn(void);</li>
<li class="new">extern bool executeTurnOff(void);</li>
</ol>
</td>
</tr><tr>
<th>onoff.c</th>
</tr><tr>
<td>
<ol>
<li class="new">#include <stdbool.h></li>
<li class="new">#include <stdio.h></li>
<li class="new">#include "object.h"</li>
<li class="new">#include "match.h"</li>
<li class="new">#include "reach.h"</li>
<li class="new">#include "toggle.h"</li>
<li class="new"></li>
<li class="new">bool executeTurnOn(void)</li>
<li class="new">{</li>
<li class="new"> OBJECT *obj = reachableObject("what you want to turn on", params[0]);</li>
<li class="new"> if (obj != NULL)</li>
<li class="new"> {</li>
<li class="new"> if (obj == lampOff)</li>
<li class="new"> {</li>
<li class="new"> toggleLamp();</li>
<li class="new"> }</li>
<li class="new"> else</li>
<li class="new"> {</li>
<li class="new"> printf(obj == lampOn ? "The lamp is already on.\n"</li>
<li class="new"> : "You cannot turn that on.\n");</li>
<li class="new"> }</li>
<li class="new"> }</li>
<li class="new"> return true;</li>
<li class="new">}</li>
<li class="new"></li>
<li class="new">bool executeTurnOff(void)</li>
<li class="new">{</li>
<li class="new"> OBJECT *obj = reachableObject("what you want to turn off", params[0]);</li>
<li class="new"> if (obj != NULL)</li>
<li class="new"> {</li>
<li class="new"> if (obj == lampOn)</li>
<li class="new"> {</li>
<li class="new"> toggleLamp();</li>
<li class="new"> }</li>
<li class="new"> else</li>
<li class="new"> {</li>
<li class="new"> printf(obj == lampOff ? "The lamp is already off.\n"</li>
<li class="new"> : "You cannot turn that off.\n");</li>
<li class="new"> }</li>
<li class="new"> }</li>
<li class="new"> return true;</li>
<li class="new">}</li>
</ol>
</td>
</tr></table>
<p>
To turn the lamp on and off,
we will use the same trick we used to open and close the door and the box
(see chapter 12).
</p>
<table class="code"><tr>
<th>toggle.h</th>
</tr><tr>
<td>