Beyond One Dimension

<BODY LANG="EN"> <HR><center> <table border=1> <td><A NAME="tex2html14" HREF="c19.shtml"><img height=36 width=36 alt="PREVIOUS" src="http://www.cs.utah.edu/icons/latex2html/previous.gif"></A></td> <td><A NAME="tex2html20" HREF="c19.shtml"><img height=36 width=36 alt="UP" src="http://www.cs.utah.edu/icons/latex2html/up.gif"></A></td> <td><A NAME="tex2html22" HREF="node2.shtml"><img height=36 width=36 alt="NEXT" src="http://www.cs.utah.edu/icons/latex2html/next.gif"></A></td> <td><a href="contents-node1.shtml"><img height=36 width=36 alt="CONTENTS" src="http://www.cs.utah.edu/icons/latex2html/toc.gif"></a></td> <td><a href="reset.hamlet"><img height=36 width=36 alt="RESET" src="http://www.cs.utah.edu/icons/latex2html/stop.gif"></a></td> <td><a href="copyright.html"><img height=36 width=36 alt="COPYRIGHT" src="http://www.cs.utah.edu/icons/latex2html/copyright.gif"></a></td> <td><a href="mailto:hamlet@cs.utah.edu"><img height=36 width=36 alt="FEEDBACK" src="http://www.cs.utah.edu/icons/latex2html/feedback.gif"></a></td> <td>     <a href="http://www.cs.utah.edu/%7Ehamlet/icons.html"><img height=36 width=36 alt=ABOUT src=http://www.cs.utah.edu/icons/latex2html/about.gif></a>  </td> </table> </center> <HR><H1><A NAME="SECTION00010000000000000000">Beyond One Dimension</A></H1> <P> We have already looked at one-dimensional arrays. They provide a means of accessing many instances of a single datatype using only one identifier. In C, we can declare arrays to be of almost any dimension. <P> The only thing tricky about multidimensional arrays crops up when you pass them as arguments to functions. Otherwise, as long as you can think in more than one dimension, you should have no problem. <P> It is easy to visualize a two-dimensional array as a table. Take a look at ``marray1.c'' in your ``examples'' directory (or <A HREF="../examples/marray1.c#marray1c">view it directly</A>). We have declared a 9x9 array which we fill up with the multiplication table. After we have filled it up, we print it out. Just as <B>for</B> loops are handy for dealing with one-dimensional arrays, doubly-nested <B>for</B> loops are handy for dealing with two-dimensional arrays. <P> What's a good way of visualizing a three-dimensional array? <P> <P><A NAME="tex2html4" HREF="answer24.html">Click here for the answer</A><P> <P> Take a look at ``marray2.c'' (or <A HREF="../examples/marray2.c#marray2c">view it directly</A>). <P> The main program declares and constructs a three-dimensional array called ``tables''. It is then filled in so that it contains an addition table, a subtraction table, and a multiplication table. (Note the three sets of doubly-nested for loops.) <P> Now take a look at the <TT>print_table</TT> function. It prints out a 9x9 arithmetic table. What kind of array argument does it expect? <P> <P><A NAME="tex2html5" HREF="answer37.html">Click here for the answer</A><P> <P> Now notice how we pass it three different two-dimensional arrays to print. We index ``tables'' only with the <B>first</B> index, which essentially ``peels off'' a two-dimensional array which we then pass as a two-dimensional argument. This is an example of how multi-dimensional arrays can be decomposed into lower-dimensional arrays. <P> If you're observant, you'll be wondering why we had to declare the exact bounds of the two-dimensional argument to <TT>print_table</TT>, since we don't have to declare the bounds of one-dimensional array arguments. Actually, we <I> don't</I> have to declare all of the bounds of a two-dimensional array. <P> Try modifying the implementation of <TT>print_table</TT> so that the declaration of table reads <P> <PRE> char table[][9]</PRE> <P> Now try compiling the program. It should compile OK. <P> Try modifying the implementation of <TT>print_table</TT> one more time so that the declaration of table reads <P> <PRE> char table[][]</PRE> <P> Try compiling it again. What happens? <P> <P><A NAME="tex2html6" HREF="answer45.html">Click here for an answer</A><P> <P> You might be wondering what happens if you make a mistake in declaring the bounds of a multi-dimensional array used as a function parameter. Try it out. Change the declaration of ``table'' in <TT>print_table</TT> to read <P> <PRE> char table[][7]</PRE> <P> Compile and run the program. 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