帮我用c语言链表写一个可以读入多行文本的KWIC索引系统

好的，我可以回答这个问题。KWIC索引系统是一种文本索引技术，可以将文本中的关键词按照一定的规则排列，方便用户查找。以下是一个基于链表的C语言实现：

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

#define MAX_LINE_LEN 1024
#define MAX_WORD_LEN 128
#define MAX_CONTEXT_LEN 40

typedef struct node {
    char *word;
    struct node *next;
} Node;

void insert(Node **head, char *word) {
    Node *new_node = (Node *)malloc(sizeof(Node));
    new_node->word = word;
    new_node->next = NULL;

    if (*head == NULL) {
        *head = new_node;
    } else {
        Node *curr = *head;
        while (curr->next != NULL) {
            curr = curr->next;
        }
        curr->next = new_node;
    }
}

void free_list(Node *head) {
    while (head != NULL) {
        Node *temp = head;
        head = head->next;
        free(temp->word);
        free(temp);
    }
}

void to_lower(char *str) {
    for (int i = 0; str[i]; i++) {
        str[i] = tolower(str[i]);
    }
}

void print_kwic(char *line, int index, int context_len) {
    char *words[MAX_WORD_LEN];
    int word_count = 0;

    // Split line into words
    char *word = strtok(line, " \t\n");
    while (word != NULL) {
        words[word_count++] = word;
        word = strtok(NULL, " \t\n");
    }

    // Print KWIC for each word
    for (int i = 0; i < word_count; i++) {
        // Shift words to the left
        for (int j = i; j < word_count + i; j++) {
            int k = j % word_count;
            if (j > i) {
                printf(" ");
            }
            printf("%s", words[k]);
        }
        // Print context
        printf("\t");
        for (int j = i - context_len; j <= i + context_len; j++) {
            int k = (j + word_count) % word_count;
            if (j == i) {
                printf("[");
            }
            printf("%s", words[k]);
            if (j == i) {
                printf("]");
            }
            if (j < i + context_len) {
                printf(" ");
            }
        }
        printf("\n");
    }
}

int main() {
    char line[MAX_LINE_LEN];
    Node *head = NULL;

    // Read lines from stdin and insert into linked list
    while (fgets(line, MAX_LINE_LEN, stdin) != NULL) {
        char *word = strdup(line);
        to_lower(word);
        insert(&head, word);
    }

    // Print KWIC for each line
    int index = 0;
    int context_len = MAX_CONTEXT_LEN / 2;
    Node *curr = head;
    while (curr != NULL) {
        printf("%d:\t", index++);
        print_kwic(curr->word, index, context_len);
        curr = curr->next;
    }

    // Free memory
    free_list(head);

    return 0;
}

这个程序可以从标准输入读入多行文本，然后对每一行进行KWIC索引，并输出到标准输出。KWIC索引的上下文长度可以通过修改`MAX_CONTEXT_LEN`宏定义来调整。