I dont understand how the insert function mechanism will be does someone get it(Having an array of linked lists as chaining should be used)?

Question

I have created an insert function that adds a students id,first name,last name and email in an array of linked list. I should create another function that checks if a certain student is available and update his email, but I don't know where to start with that function

HEADER FILE

#pragma once
#include <iostream>
#include <string>
using namespace std;
class HashTable
{
private:
    struct HashNode
    {
        string key;
        string value;
        HashNode* next;
    };
    HashNode* table[100];
    int currentSize;
    int maxSize;
public:
    HashTable(int x);
    void insert(string ID, string firstName, string lastName, string email);
    bool update(string ID, string newEmail);
};

CPP FILE

HashTable::HashTable(int x)
{
    maxSize = x;
};


 void HashTable::insert(string ID, string firstName, string lastName, string email)
{
    HashNode x;
    x.key = ID;
    x.value = firstName + " " + lastName + " " + email;
    int index = hash(x.key);
    if (*(table + index) == NULL)
    {
        *(table + index) = new HashNode;
        (*(table + index))->key = x.key;
        (*(table + index))->value = x.value;
        (*(table + index))->next = NULL;
    }
    else
    {
        HashNode* temp = *(table + index);
        while (temp->next != NULL)
            temp = temp->next;
        HashNode* newNode = new HashNode;
        newNode->key = x.key;
        newNode->value = x.value;
        newNode->next = NULL;
        temp->next = newNode;
        temp = NULL;
        newNode = NULL;
    }
    currentSize++;
};

Answer 1

1. You should store firstName , lastName and email as three separate string fields in HashNode instead of concatenating them in insert . That will save you numerous headaches.

2. In update function, you need to scan the linked list the student was (or could be) added to; that is, that starting at table[hash(ID)] (btw, table[index] is the same as *(table + index) , at least for pointers [arrays are often treated as pointers in C and C++]). You need to find the node having the key you look for (if any), and update its email.