这道练习题训练了：
1.结构体数组
2.二分查找
3.指针操作
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都不难。但非常基础，我认为非常好，做完了记到博客上来，题目见k&R，实现例如以下：
/*
* Practice of struct array. K&R 6-1
* @author : wusuopubupt
* @date : 2014-09-18
*/
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#define MAXWORD 100
typedef struct key_{
char *word;
int count;
} key;
key key_tab[] = {
{"auto", 0},
{"break", 0},
{"case", 0},
{"char", 0},
{"const", 0},
{"continue", 0},
{"default", 0},
{"for", 0},
{"int", 0},
{"void", 0},
{"while", 0}
};
int getword(char *word, int n);
int binary_search(key key_tab[], char *word, int n);
key *binary_search2(key *key_tab, char *word, int n);
int getword(char *word, int n) {
int c;
char *w = word;
while(isspace(c = getchar())) {
;
}
if(c != EOF) {
*w++ = c;
}
if(!isalpha(c)) {
*w = ' ';
return c;
}
while(n > 0) {
c = getchar();
if(isalnum(c)) {
*w++ = c;
}
else {
break;
}
n--;
}
*w = ' ';
return w[0];
}
int binary_search(key key_tab[], char *word, int n) {
int low = 0;
int high = n-1;
int mid;
int result;
while(low <= high) {
mid = (low+high) / 2;
result = strcmp(word, key_tab[mid].word);
if(result < 0) {
high = mid-1;
}
else if(result > 0) {
low = mid + 1;
}
else {
return mid;
}
}
return -1;
}
/* implemented with pointer */
key *binary_search2(key *key_tab, char *word, int n) {
key *low = key_tab;
key *high = key_tab + n-1;
key *mid;
int result;
while(low <= high) {
//mid = (low+high) / 2; /* error: can not use pointer+pointer d*/
mid = low + (high-low) / 2; /* pointer + num */
result = strcmp(word, mid->word);
if(result < 0) {
high = mid-1;
}
else if(result > 0) {
low = mid + 1;
}
else {
return mid;
}
}
return NULL;
}
int main1() {
int i;
int n_keys = sizeof(key_tab) / sizeof(key_tab[0]);
char word[MAXWORD];
while(getword(word, MAXWORD) != EOF) {
if(isalpha(word[0])) {
if((i = binary_search(key_tab, word, n_keys)) >= 0) {
key_tab[i].count++;
}
}
}
i = 0;
while(i < n_keys) {
printf("%s : %d
", key_tab[i].word, key_tab[i].count);
i++;
}
return 0;
}
int main() {
int n_keys = sizeof(key_tab) / sizeof(key_tab[0]);
char word[MAXWORD];
key *k = NULL;
while(getword(word, MAXWORD) != EOF) {
if(isalpha(word[0])) {
if((k = binary_search2(key_tab, word, n_keys)) != NULL) {
k->count++;
}
}
}
int i = 0;
while(i < n_keys) {
printf("%s : %d
", key_tab[i].word, key_tab[i].count);
i++;
}
return 0;
}