Page 115 - Programming Microcontrollers in C

100 Chapter 2 Advanced C Topics

word of the node), it is necessary to either traverse to the node on the
left or add a new node on the left if there is none there. The code
p->left = addtree(p->left,w);

does exactly what is needed in this case. This recursive call to
addtree() will descend to the left Tnode if one exists. If one does
not exist, the pointer to the left Tnode will be NULL, so addtree()
will create a new node for this location. addtree() returns a pointer
to the new node, so it will be placed in the left pointer of this node.
Had the lexical value of the word been greater than that of the
word stored in the node, the addtree() call would work on the
pointer to the right child node. Therefore, the function addtree()
will start at the root node and traverse down the tree to the right or
left child nodes depending on the size of the word relative to the
sizes of the words in the tree. If the word is found in the tree, its
count is incremented. If control proceeds down the tree, and the word
is not found, eventually, a Tnode with a NULL pointer to the direc­
tion that the path must move. A that time a new Tnode is created
and the word is assigned to that Tnode.
When all of the data to be input into the tree are read in, control
is passed to the function treeprint(). The argument of
treeprint() is a pointer to the root node and treeprint()
returns nothing to the calling program. Efficient printing out of the
data requires another recursive routine. The function treeprint()
shown below shows this routine. treeprint() is called with the
root pointer as an argument. The root pointer will not be a NULL, so
the code following the if statement will be executed. The first

/* treeprint: in-order print of tree p */

void treeprint(TNODE *p)
{
if(p !=NULL)
{
treeprint(p->left);
printf(“%4d%15s\n”,p->count,p->word);
treeprint(p->right);
}
}