单词反序

/* 程序功能：用户输串单词，完成单词的反序, 并计算单词的长度.
 * 如：I Love China, 将其变为 China Love I.
 *
 * 解题思路：
 * 1.首先将整个字符串倒置，如 anihC evoL I
 * 2.再遍历每个单词，将其倒置
 *
 * 程序说明：该程序只考虑用户输入的大小写，其它字符默认转换成空格处理.
 * 创建时间:2014-10-31
 * 作者：elijah
 * */

#include <stdio.h>

#define BUFF_SIZE 1024
#define IS_LETTER(ch) ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z'))

int get_data(char *dest, int num);
int reverse_words(char *str);
void swap(char *head, char *tail);

int main()
{
    char buf[BUFF_SIZE];
    int length;
    length = get_data(buf, BUFF_SIZE);
    reverse_words(buf);
    puts(buf);
    printf("length = %d\n", length);

    return 0;
}

void swap(char *head, char *tail)
{
    while (head < tail) {
        *head ^= *tail;
        *tail ^= *head;
        *head++ ^= *tail--;
    }
}

int reverse_words(char *str)
{
    char *head = str,
         *tail = str;

    while ('\0' != *tail)    /*将尾指针定位到字符串的尾部*/
        tail++;

    swap(head, tail - 1);    /*将整个字符串倒置*/

    while ('\0' != *head) {

        while (32 == *head) /*找单词的头*/
            head++;
        tail = head;

        while (32 != *tail && '\0' != *tail)    /*找到单词的末尾*/
            tail++;
        swap(head, tail - 1);
        head = tail;    /*将头指向尾, 为下次做准备*/
    }

    return 0;
}

int get_data(char *dest, int num)
{
    char ch;
    int count = 0;

    /*校验模块*/
    if (NULL == dest || num < 1)
        return -1;

    while ('\n' != (ch = getchar()) && count < num - 1) {
        /*使用宏函数判断用户输入*/
        if (!IS_LETTER(ch))
            ch = 32;
        dest[count++] = ch;
    }
    dest[count] = '\0';

    return count;
}