Page 112 - Programming Microcontrollers in C

Structures 97

The first two elements to this structure are a pointer to the word
contained in the node, and the number of times that the word has
been seen. The last two elements are pointers to structures of the
type struct tnode. Note that in the typedef of the struct
tnode, the structure tag was used. It is necessary to use the tag in
this case because the self-referential pointers inside of the structure
needs the tag to find the correct type. For the remainder of the pro­
gram, the typedef Tnode is used.
Some new files are included in the include files. These files will
be discussed in a following section. The first is ctype.h. This pro­
gram uses several character tests that are identified in ctype.h.
There are string operations found in string.h , and there are stan­
dard functions defined in stdlib.h.

#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>

The list of function prototypes for the functions written in this
program follow:

Tnode *addtree(TNODE *, char *);
Tnode *talloc(void);
void treeprint( TNODE *);
int getword(char *, int);
char *strsave(char *);
The first function is the function that is used to add a tree to the
program. *talloc() is a function that allocates memory for a
Tnode. The function treeprint() prints out the tree, and
getword() reads in a word from the input stream. There are two
function prototypes defined within the program getword().These
functions are used by getword() only. The final function above
saves the string pointed to by the argument in a safe place and re­
turns a pointer to the word location in memory.
The main program is relatively simple. The constant MAXWORD
is the maximum number of characters that can be allowed in a word.
Within main() a pointer to a structure Tnode named root is de­
clared along with a character array named word and an integer i.