算法：编程在一个已知的字符串中查找最长单词，假定字符串中只包含字母和空格，空格用来分隔不同单词

#include "stdio.h"
#include "string.h"
int main(void)
{
    //定义两个数组，sentence储存字符串，word存储单词
    char sentence[1024] = {}, word[64] = {};
    //length：单词长度；index：字符串下标
    int length = 0, index = 0;
    int max = 0, k = 0;
    printf("please input a sentence:");
    //fgets():从键盘获取字符串
    fgets(sentence, 1024, stdin);
    //循环直到字符串结束
    for (int i = 0; sentence[i] != '\0'; i++)
    {
        length = 0;
        //获取一个单词的长度
        for (k = i; sentence[k] != ' ' && sentence[k] != '\0'; k++)
        {
            length++;
            index++;
        }
        //判断当前单词长度是否大于已判断的最大单词长度
        if (length >= max)
        {
            //清空word数组
            memset(word, '\0', sizeof(max));
            max = length;
            for (int j = 0; j<length; j++)
            {
                word[j] = sentence[index - length + j];
            }
            index++;
            i = k;
        }
    }
    puts(word);
    return 0;
}