我的程序通过getchar（）读取输入，使用二叉树结构保存每个单词的出现次数，然后在最后打印它们。任何只包含数字、下划线和字母且不以数字开头的非空字符集都算作一个单词。当我把First_word First_word First_word Second_word Third_word Forth_word这一行放在一个名为file.input的文件中，并通过命令./a.out <file.input运行程序时，我得到的输出是：3 First_word虽然应该有其他的词。
我已经测试过了，getword和print工作正常。这是我写的代码：

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

struct bt_node {
    char *word;
    int count;
    struct bt_node *left;
    struct bt_node *right;
};

int main()
{
    extern struct bt_node *first;
    int getword(char *, int);
    struct bt_node *search(char *word, struct bt_node *node), *node = NULL;
    void print(struct bt_node *node);

    int lim = 100;
    char word[lim];

    while (getword(word, lim) != EOF) {
        if (!(isalpha(word[0]) || word[0] == '_'))
            continue;
        search(word, node)->count++;
        node = first;
    }
    
    print(first);

    return 0;
}

void print(struct bt_node *node)
{
    if (node->left != NULL)
        print(node->left);
    printf("%4d\t%s\n", node->count, node->word);
    if (node->right != NULL)
        print(node->right);
}

struct bt_node *search(char *word, struct bt_node *node)
{
    struct bt_node *generate_node(char *word);
    if (node == NULL)
        node = generate_node(word);

    int comp = strcmp(word, node->word);
    if (comp == 0)
        return node;
    else
        return search(word, 0 < comp ? node->right : node->left);
}

int getword(char *word, int lim)
{
    int c, temp, getch(void);
    void ungetch(int);
    char *w = word;

    pass_space: /* if encountered a comment or string skip it and go back to this step */
    while (isspace(c = getch()))
        ;
    if (c == '/') {
        if ((temp = getch()) == '*') { 
            while ((c = getch()) != EOF)
                if (c == '*' && (c = getch()) == '/')
                    goto pass_space;
                else if (c == '*')
                    ungetch(c);
        } else
            ungetch(temp);
    } else if (c == '\"') {
        while ((c = getch()) != EOF)
            if (c == '\"')
                goto pass_space;
    }
    if (c != EOF)
        *w++ = c;
    if (!isalpha(c) && c != '_') {
        *w = '\0';
        return c;
    }
    for ( ; --lim > 0; w++)
        if (!isalnum(*w = getch()) && *w != '_') {
            ungetch(*w);
            break;
        }
    *w = '\0';
    return word[0];
}

#define BUFSIZE 100

int buf[BUFSIZE];
char bufp = 0;

int getch(void)
{
    return bufp > 0 ? buf[--bufp] : getchar();
}

void ungetch(int c)
{
    if (bufp < BUFSIZE)
        buf[bufp++] = c;
    else
        printf("ungetch: too many characters, didn't unread %c\n", c);
}

struct bt_node *generate_node(char *word)
{
    struct bt_node *bt_alloc(void);
    char *alloc_char(int);
    
    struct bt_node *node = bt_alloc();
    node->word = alloc_char(strlen(word)+1);
    strcpy(node->word, word);
    node->count = 0;
    node->left = NULL;
    node->right = NULL;

    return node;
}

#define BTALLOCSIZE 10000

static struct bt_node bt_allocbuf[BTALLOCSIZE];
static struct bt_node *bt_allocp = bt_allocbuf;

struct bt_node *first = bt_allocbuf;

struct bt_node *bt_alloc(void)
{
    if (bt_allocp <= bt_allocbuf + BTALLOCSIZE)
        return bt_allocp++;
    else {
        printf("bt_alloc - error: can't allocate\n");
        return NULL;
    }
}

#define ALLOCSIZE 10000

static char char_allocbuf[ALLOCSIZE];
static char  *char_allocp = char_allocbuf;

char *alloc_char(int n)
{
    if (char_allocbuf + ALLOCSIZE - char_allocp >= n) {
        char_allocp += n;
        return char_allocp - n;
    } else {
        printf("alloc_char - error: can't allocate\n");
        return NULL;
    }
}