統計輸入中關鍵詞出現的次數（二分查找實現）

/* 統計輸入的c語言中關鍵詞出現的次數
 * @method: 使用二分查找實現，keytab[]關鍵詞必須是按首字母排好序的關鍵詞表
 */

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

struct key
{
	char *word;
	int count;
} keytab[] = {
        "char", 0,
		"int", 0,
		"void", 0
};


#define MAXWORD 		100
#define NKEYS 	(sizeof keytab / sizeof keytab[0])
int getword(char *, int);
int binsearch(char *, struct key *, int);

main()
{
	int n;
	char word[MAXWORD];
	
	while(getword(word, MAXWORD) != EOF)
		if(isalpha(word[0]))
			if((n = binsearch(word, keytab, NKEYS)) >= 0)
				keytab[n].count++;
	for(n = 0; n < NKEYS; n++)
		//if(keytab[n].count > 0)
			printf("%4d %s\n", keytab[n].count, keytab[n].word);
	return 0;
}

/* 根據首字母順序進行二分查找，tab[]必須是有序的 */
int binsearch(char *word, struct key tab[], int n)
{
	int cond;
	int low, high, mid;
	low = 0;
	high = n-1;
	while(low <= high)
	{
		mid = (low+high)/2;
		if((cond = strcmp(word, tab[mid].word)) < 0)
			high = mid - 1;
		else if(cond > 0)
			low = mid + 1;
		else
			return mid;
	}
	return -1;
}

/* 從輸入中讀取下一個單詞*/
int getword(char *word, int lim)
{
	int c;
	//void ungetch(int);
	char *w = word;
	
	while(isspace(c = getchar())) //檢查參數c是否爲空格字符,即爲下一個字母的開始
		;
	if(c != EOF)
		*w++ = c;
	if(!isalpha(c)) //判斷字符變量c是否爲字母
	{
		*w = '\0';
		return c;
	}
	for(; --lim > 0; w++)
		if(!isalnum(*w = getchar())) //判斷字符變量c是否爲字母或數字
		{
			//ungetch(*w);
			break;
		}
	*w = '\0';
	return word[0];
}