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   6 <title>Assignment #2</title>
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   9 <H1>Assignment #2</H1>
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  15 <B>Intermediate C Programming
  16 <br>
  17 <br>
  18 UW Experimental College
  19 </B><br>
  20 <br>
  21 <B>Assignment #2
  22 </B><p><B>Handouts:
  23 </B></p><p><a href="PS2.html">Assignment #2</a>
  24 <br><a href="PS1a.html">Assignment #1 Answers</a>
  25 <br><a href="http://www.eskimo.com/~scs/cclass/int/sx2.html">Class Notes, Chapter 16</a>
  26 <br><a href="http://www.eskimo.com/~scs/cclass/int/sx3.html">Class Notes, Chapter 17</a>
  27 <p><B>Review Questions:
  28 </B></p><OL><li>List some differences between text and binary data files.
  29 </OL><p><B>Exercises:
  30 </B></p><OL><li>We're going to fix one of the more glaring deficiencies
  31 of the initial implementation of the game,
  32 namely that the description of the dungeon takes the form of
  33 hard-compiled structure arrays in <TT>main.c</TT>,
  34 such that the source code must be edited
  35 (and in a tedious way, at that)
  36 and the game recompiled
  37 whenever we want to modify the dungeon.
  38 (We're used to recompiling when we make changes to our programs,
  39 but we shouldn't have to recompile when we make expected changes to our data.
  40 Imagine if a spreadsheet program
  41 required you to enter your worksheet expressions or data
  42 with a C compiler and recompile each time!)
  43 <br>
  44 <br>
  45 We're going to add code which can read the dungeon description
  46 dynamically, at run time, from a simple, textual data file.
  47 The file will describe the rooms,
  48 the objects and which rooms they're initially in,
  49 and the exits which interconnect the rooms.
  50 As the file is read,
  51 we'll dynamically assign new instances
  52 of <TT>struct room</TT> and <TT>struct object</TT>
  53 to define the rooms and objects which the data file describes.
  54 We won't know how many room and object structures we'll need,
  55 and we certainly won't know what descriptions they will contain,
  56 so we'll abandon the <TT>rooms</TT> and <TT>objects</TT> arrays from <TT>main.c</TT>,
  57 along with their cumbersome initializations.
  58 We'll add (in <TT>objects.c</TT>) an allocation function,
  59 <TT>newobject()</TT>,
  60 which will return a pointer to a brand-new object structure
  61 which we can use to contain some new object,
  62 usually one
  63 we've just read from the data file.
  64 Similarly, we'll add a <TT>newroom()</TT> function to <TT>rooms.c</TT>
  65 which will return a pointer to a brand-new room structure.
  66 (We're not quite ready to do full-blown dynamic memory allocation yet,
  67 so for now, the room and object alloction functions
  68 will dole structures out of fixed-size arrays
  69 which we'll arbitrarily declare as having size 100.
  70 Naturally we'll keep track of how many structures are actually in use,
  71 and complain if an attempt is made to use more than 100.
  72 Since the allocation code is isolated
  73 down within <TT>rooms.c</TT> and <TT>object.c</TT>,
  74 only those modules will need rewriting
  75 when we move to a more flexible allocation scheme;
  76 the code which calls <TT>newroom()</TT>
  77 and <TT>newobject()</TT> won't need to change.)
  78 <br>
  79 <br>
  80 Appended to this assignment is a listing of a new file, <TT>io.c</TT>,
  81 for doing the data file reading.
  82 (This code is also on the disk
  83 or at the ftp site,
  84 in the <TT>week2</TT> subdirectory.)
  85 <br>
  86 <br>
  87 Rip out the definitions and initializations of the <TT>objects</TT>
  88 and <TT>rooms</TT> arrays at the top of <TT>main.c</TT>;
  89 also remove the initialization of <TT>actor</TT>
  90 (but leave the definition).
  91 At the top of <TT>main()</TT>,
  92 before the initial call to <TT>listroom</TT>,
  93 add the lines
  94 <pre>
  95         if(!readdatafile())
  96                 exit(1);
  97
  98         gotoroom(&amp;actor, getentryroom());   /* put actor in initial room */
  99 </pre>
 100 <br>
 101 <br>
 102 Add the following code to <TT>object.c</TT>
 103 (it can go near the top):
 104 <pre>
 105 #define MAXOBJECTS 100
 106
 107 static struct object objects[MAXOBJECTS];
 108 static int nobjects = 0;
 109
 110 struct object *
 111 newobject(char *name)
 112 {
 113 struct object *objp;
 114
 115 if(nobjects &gt;= MAXOBJECTS)
 116         {
 117         fprintf(stderr, "too many objects\n");
 118         exit(1);
 119         }
 120
 121 objp = &amp;objects[nobjects++];
 122
 123 strcpy(objp-&gt;name, name);
 124 objp-&gt;lnext = NULL;
 125
 126 return objp;
 127 }
 128 </pre>
 129 (This code is in the file <TT>object.xc</TT>
 130 in the <TT>week2</TT> subdirectory.)
 131 <br>
 132 <br>
 133 Add the following code to <TT>rooms.c</TT>
 134 (it can go near the top):
 135 <pre>
 136 #define MAXROOMS 100
 137
 138 static struct room rooms[MAXROOMS];
 139 static int nrooms = 0;
 140
 141 struct room *
 142 newroom(char *name)
 143 {
 144 struct room *roomp;
 145 int i;
 146
 147 if(nrooms &gt;= MAXROOMS)
 148         {
 149         fprintf(stderr, "too many rooms\n");
 150         exit(1);
 151         }
 152
 153 roomp = &amp;rooms[nrooms++];
 154
 155 strcpy(roomp-&gt;name, name);
 156 roomp-&gt;contents = NULL;
 157 for(i = 0; i &lt; NEXITS; i++)
 158         roomp-&gt;exits[i] = NULL;
 159
 160 return roomp;
 161 }
 162
 163 struct room *
 164 findroom(char *name)
 165 {
 166 int i;
 167
 168 for(i = 0; i &lt; nrooms; i++)
 169         {
 170         if(strcmp(rooms[i].name, name) == 0)
 171                 return &amp;rooms[i];
 172         }
 173
 174 return NULL;
 175 }
 176
 177 struct room *
 178 getentryroom(void)
 179 {
 180 if(nrooms == 0)
 181         return NULL;
 182 return &amp;rooms[0];   /* temporary */
 183 }
 184 </pre>
 185 (This code is in the file <TT>rooms.xc</TT>
 186 in the <TT>week2</TT> subdirectory.)
 187 <br>
 188 <br>
 189 You'll also need the file <TT>fgetline.c</TT>,
 190 which is appended behind the new <TT>io.c</TT>,
 191 and also in the <TT>week2</TT> subdirectory.
 192 <br>
 193 <br>
 194 After adding all the new code,
 195 and any necessary prototype declarations to <TT>game.h</TT>,
 196 the program should again compile and run,
 197 but it will expect to find a data file named
 198 <TT>dungeon.dat</TT> in the current directory.
 199 A sample <TT>dungeon.dat</TT> file
 200 (corresponding to the old, hard-compiled game)
 201 is included here
 202 (and in the <TT>week2</TT> subdirectory).
 203 Once you see how it works, you can start extending the dungeon
 204 simply by modifying the <TT>dungeon.dat</TT> file.
 205 <li>(tricky)
 206 If you added long descriptions to rooms and objects last week,
 207 devise and implement a way for those long descriptions to be
 208 read from the data file.
 209 <li>(easier)
 210 Expand the set of allowable exits from rooms.
 211 Add the possibility of northeast, southeast, northwest, and
 212 southwest exits, or ``up'' and ``down''
 213 exits, or all six.
 214 Add commands to go in these new directions.
 215 Modify the data file reading code in <TT>io.c</TT> to handle
 216 setting up the new exits.
 217 </OL><hr>
 218 <hr>
 219 <p>
 220 This page by <a href="http://www.eskimo.com/~scs/">Steve Summit</a>
 221 // <a href="copyright.html">Copyright</a> 1995-9
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