Singly linked list implements word index table (C language)

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>
#define N 30
typedef struct WORD{//Save all words starting with value, words starting with different letters
    struct WORD    *next;
    char        *word;
} Word;


typedef struct NODE{//Save all words
    struct NODE *next;
    char letter;
    Word* data;
} Node;
int insert(Node **rootp,char *str);
void print(Node* rootp);
int main (void)
{
    Node* p1=(Node*)malloc(sizeof(Node));
    if(p1==NULL)
    perror("malloc error");

    p1->next=NULL;
    p1->letter='a';
    Word* the_word;
    the_word=(Word*)malloc(sizeof(Word));
    if(the_word==NULL)
    perror("malloc error");
    
    the_word->next=NULL;
    
    the_word->word=(char*)malloc(N);
    if(the_word->word=NULL)
    perror("malloc error");
    
    the_word->word="ahello";
    
    p1->data=the_word;
    
    char value[N];
    printf("Enter the inserted string:\n");
    while(fgets(value,N,stdin)!=NULL)
    {
        value[strlen(value)-1]='\0';//Process the newline character read by fgets into a terminator
        insert(&p1,value);
    }
    
    
    print(p1);
    
}
int insert(Node **rootp,char *the_word)
{
    Node* current_node;
    Word* current_word;
    Word** wordlink;
    int first_letter;
    Word* new_word;
    Node* new_node;
    int num;
    
    first_letter=*the_word;//Get the first character of the inserted string
    if(isalpha(first_letter)==0) //If the first character is not a letter, return on error
    return -1;
    
    while((current_node=*rootp)!=NULL&¤t_node->letter<first_letter)
    rootp=¤t_node->next;
    
    /*If current_node==NULL or the letter in the current node is greater than or equal to first_letter, jump out of the loop*/
    if(current_node==NULL||current_node->letter>first_letter)
    /* If the current node is NULL, or the character index of the current node is greater than first_letter
    Create a new node and insert into the index table */
    {
    new_node=(Node*)malloc(sizeof(Node));
    if(new_node==NULL)
    return -1;
    
    new_node->letter=first_letter;//Insert the node into the index table
    new_node->next=current_node;
    new_node->data=NULL;
    *rootp=new_node;
    current_node=new_node;
    /*Assign the newly inserted node to current_node*/
    }
    
    wordlink=¤t_node->data;//Handle the case where the characters in the index table are equal to the characters you want to insert
    while((current_word=*wordlink)!=NULL)
    //Insert words in the secondary linked list, first find the insertion position
    {
        num=strcmp(current_word->word,the_word);
        if(num>=0)
        break;
        wordlink=¤t_word->next;
    }
    if(current_word!=NULL&&num==0)//current_word is not empty, and num is 0, then word already exists
    return -1;
    
    new_word=(Word*)malloc (sizeof( Word));
    if(new_word==NULL)
    return -1;
    
    new_word->word=(char*)malloc(strlen(the_word)+1);//Allocate space for words
    if(new_word->word==NULL)
    return -1;
    
    strcpy(new_word->word,the_word);//Insert the word into the secondary linked list
    new_word->next=current_word;
    *wordlink=new_word;
    return 0;
}
void print(Node* rootp)
{
    assert(rootp);
    Node* tmp=rootp;
    Word* word_tmp;
    while(tmp!=NULL)
    {
        word_tmp=tmp->data;
        printf("%c-------%c\n\n",tmp->letter,tmp->letter);
        while(word_tmp!=NULL)
        {
            printf("%s-->",word_tmp->word);
            word_tmp=word_tmp->next;
        }
        printf("NULL\n");
    printf("%c-------%c\n\n",tmp->letter,tmp->letter);
        tmp=tmp->next;
    }
    
}