单词计数 hello

The C Program Language 6.5节

统计所用输入单词出现的次数，为啥遍历会出现错误

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

#define MAXWORD 100
struct tnode{
    char *word;
    int count;
    struct tnode *left;
    struct tnode *right;
};

struct tnode *addtree(struct tnode*, char *);
void treeprint(struct tnode*);
int getword(char *, int);

int main()
{
    struct tnode *root;
    char word[MAXWORD];  
    root = NULL;
    while(getword(word, MAXWORD) != EOF)
        if(isalpha(word[0]))
            root = addtree(root, word);
    treeprint(root);
   // printf("%d\n", num);
    getchar(); 
    return 0;
}

struct tnode *talloc()
{
    return (struct tnode *)malloc(sizeof(struct tnode));
}
 
struct tnode* addtree(struct tnode *p, char *w)
{
    int cond;
    if(p == NULL)
    {
        p = talloc();
        p->word = strdup(w);
        p->count = 1;
        p->left = p->right = NULL;
    }
    else if((cond=strcmp(w, p->word)) == 0)
        p->count++;
    else if(cond < 0)
        p->left = addtree(p->left, w);
    else
        p->right = addtree(p->right, w);   
    return p;
}

void treeprint(struct tnode *p)
{
    if(p != NULL)
    {
        treeprint(p->left);
        printf("%s %4d\n", p->count, p->word);
        //num++;
        treeprint(p->right);
    }      
}

#define BUFFSIZE 100
char buf[BUFFSIZE];
int bufp = 0;
int getch()
{
    return bufp>0 ? buf[--bufp] : getchar();
}

void ungetch(int c)
{
    if(bufp > BUFFSIZE)
        printf("ungetch: too many characters\n");
    else
        buf[bufp++] = c;
}

int getword(char *word, int lim)
{
    int c;
    char *w = word;
    while(isspace(c = getch()))
        ;
    if(c != EOF)
        *w++ = c;
    if(!isalpha(c))
    {
        *w = '\0';
        return c;
    }
    for(; --lim>0; w++)
        if(!isalnum(*w = getch()))
        {
            ungetch(*w);
            break;
        }
    *w = '\0';
    return word[0];
}