请给出一个可以运行的C语言代码，选择合适的散列函数和冲突处理方法，编程实现QQ账户申请与登录

以下是一个简单的哈希表实现，使用链式哈希表解决哈希冲突的问题。其中，散列函数采用了除留余数法，但可以根据实际需求进行修改。

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

#define MAX_ACCOUNTS 1000
#define HASH_SIZE 100

typedef struct account_t {
    char username[20];
    char password[20];
} Account;

typedef struct node_t {
    Account data;
    struct node_t* next;
} Node;

Node* hash_table[HASH_SIZE];

unsigned int hash(const char* str) {
    unsigned int hash = 0;
    while (*str) {
        hash = (hash * 31 + *str) % HASH_SIZE;
        str++;
    }
    return hash;
}

void insert_account(Account new_account) {
    unsigned int index = hash(new_account.username);
    Node* new_node = (Node*)malloc(sizeof(Node));
    new_node->data = new_account;
    new_node->next = hash_table[index];
    hash_table[index] = new_node;
}

Account* find_account(const char* username) {
    unsigned int index = hash(username);
    Node* curr = hash_table[index];
    while (curr) {
        if (strcmp(curr->data.username, username) == 0) {
            return &(curr->data);
        }
        curr = curr->next;
    }
    return NULL;
}

int main() {
    int choice;
    Account new_account;
    while (1) {
        printf("1. Register\n2. Login\n3. Exit\n");
        scanf("%d", &choice);
        switch (choice) {
            case 1:
                printf("Enter username: ");
                scanf("%s", new_account.username);
                printf("Enter password: ");
                scanf("%s", new_account.password);
                insert_account(new_account);
                printf("Account registered successfully.\n");
                break;
            case 2:
                printf("Enter username: ");
                scanf("%s", new_account.username);
                printf("Enter password: ");
                scanf("%s", new_account.password);
                Account* found = find_account(new_account.username);
                if (found && strcmp(found->password, new_account.password) == 0) {
                    printf("Login successful.\n");
                } else {
                    printf("Invalid username/password.\n");
                }
                break;
            case 3:
                exit(0);
            default:
                printf("Invalid choice.\n");
        }
    }
    return 0;
}