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   9 <title>section 6.1: Basics of Structures</title>
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  15 <H2>section 6.1: Basics of Structures</H2>
  16
  17 <p>Don't get too excited about the prospect of doing graphics
  18 in C--there's
  19 no one standard or portable way of doing it,
  20 so the points and rectangles we're going to be discussing
  21 must remain abstract for now
  22 (we won't be able to plot them out).
  23 </p><p>page 128
  24 </p><p>To summarize the syntax of structure declarations:
  25 A structure declaration has about four parts,
  26 most of them optional:
  27 the keyword <TT>struct</TT>,
  28 a <dfn>structure tag</dfn> (optional),
  29 a brace-enclosed list of declarations for the
  30 <dfn>members</dfn>
  31 (also called ``fields'' or ``components'')
  32 of the structure (optional),
  33 and a list of variables of the new structure type (optional).
  34 The arrangement looks like this:
  35 <pre>   struct <I>tag</I> {
  36                 <I>member declarations</I>
  37         } <I>declared variables</I> ;
  38 </pre>Normally, a structure declaration defines either a tag and the members,
  39 or some variables based on an existing tag,
  40 or sometimes all three at once.
  41 That is,
  42 we might first declare a structure:
  43 <pre>   struct point {                  /* 1 */
  44                 int x;
  45                 int y;
  46         };
  47 </pre>and then some variables of that type:
  48 <pre>   struct point here, there;       /* 2 */
  49 </pre>Or, we could combine the two:
  50 <pre>   struct point {                  /* 3 */
  51                 int x;
  52                 int y;
  53         } here, there;
  54 </pre>The list of members
  55 (if present)
  56 describes what the new structure ``looks like inside.''
  57 The list of variables
  58 (if present)
  59 is
  60 (obviously)
  61 the list of variables of this new type
  62 which we're defining
  63 and which the rest of the program will use.
  64 The tag
  65 (if present)
  66 is just an arbitrary name for the structure type itself
  67 (not for any variable we're defining).
  68 The tag is used to associate a structure definition
  69 (as in fragment 1)
  70 with a later declaration of variables of that same type
  71 (as in fragment 2).
  72 </p><p>One thing to beware of:
  73 when you declare the members of a structure without defining any variables,
  74 always remember
  75 the trailing semicolon,
  76 as shown
  77 in fragment 1
  78 above.
  79 (If you forget it,
  80 the compiler will wait until the next thing it finds in your source file,
  81 and try to define <em>that</em>
  82 as a variable or function of the structure type.)
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  92 This page by <a href="http://www.eskimo.com/~scs/">Steve Summit</a>
  93 // <a href="copyright.html">Copyright</a> 1995, 1996
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