Programming: C++ Program to Implement Hash Table

What is hash table ?
Do not confuse this with Hash List or Hash Tree.
From Wikipedia about hash table

In computing, a hash table (hash map) is a data structure used to implement an associative array, a structure that can map keys to values. A hash table uses a hash function to compute an index into an array of buckets or slots, from which the desired value can be found.

Ideally, the hash function will assign each key to a unique bucket, but it is possible that two keys will generate an identical hash causing both keys to point to the same bucket. Instead, most hash table designs assume that hash collisions—different keys that are assigned by the hash function to the same bucket—will occur and must be accommodated in some way.

This C++ Program demonstrates operations on Hash Tables

Here is source code of the C++ Program to demonstrate Hash Tables. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

/*
 *C++ Program to Implement Hash Tables
 */
#include
#include
#include
#include
using namespace std;
const int TABLE_SIZE = 128;
 
/*
 * HashEntry Class Declaration
 */
class HashEntry
{
    public:
        int key;
        int value;
        HashEntry(int key, int value)
        {
            this->key = key;
            this->value = value;
        }
};
 
/*
 * HashMap Class Declaration
 */
class HashMap
{
    private:
        HashEntry **table;
    public:   
        HashMap()
	{
            table = new HashEntry * [TABLE_SIZE];
            for (int i = 0; i< TABLE_SIZE; i++)
            {
                table[i] = NULL;
            }
        }
        /*
         * Hash Function
         */
        int HashFunc(int key)
        {
            return key % TABLE_SIZE;
        }
        /*
         * Insert Element at a key
         */
	void Insert(int key, int value)
	{
            int hash = HashFunc(key);
            while (table[hash] != NULL && table[hash]->key != key)
            {
                hash = HashFunc(hash + 1);
            }
            if (table[hash] != NULL)
                delete table[hash];
            table[hash] = new HashEntry(key, value);
	}
        /*
         * Search Element at a key
         */
        int Search(int key)
	{
	    int  hash = HashFunc(key);
	    while (table[hash] != NULL && table[hash]->key != key)
	    {
	        hash = HashFunc(hash + 1);
	    }
	    if (table[hash] == NULL)
	        return -1;
	    else
	        return table[hash]->value;
        }
 
        /*
         * Remove Element at a key
         */
        void Remove(int key)
	{
	    int hash = HashFunc(key);
	    while (table[hash] != NULL)
	    {
	        if (table[hash]->key == key)
	            break;
	        hash = HashFunc(hash + 1);
	    }
            if (table[hash] == NULL)
	    {
                cout<<"No Element found at key "<>choice;
        switch(choice)
        {
        case 1:
            cout<<"Enter element to be inserted: ";
            cin>>value;
            cout<<"Enter key at which element to be inserted: ";
            cin>>key;
            hash.Insert(key, value);
            break;
        case 2:
            cout<<"Enter key of the element to be searched: ";
            cin>>key;
            if (hash.Search(key) == -1)
            {
	        cout<<"No element found at key "<>key;
            hash.Remove(key);
            break;
        case 4:
            exit(1);
        default:
           cout<<"\nEnter correct option\n";
       }
    }
    return 0;
}

$ g++ hash_table.cpp
$ a.out
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 1
Enter element to be inserted: 12
Enter key at which element to be inserted: 1
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 1
Enter element to be inserted: 24
Enter key at which element to be inserted: 2
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 1
Enter element to be inserted: 36
Enter key at which element to be inserted: 3
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 1
Enter element to be inserted: 48
Enter key at which element to be inserted: 4
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 1
Enter element to be inserted: 60
Enter key at which element to be inserted: 5
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 2
Enter key of the element to be searched: 3
Element at key 3 : 36
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 2
Enter key of the element to be searched: 5
Element at key 5 : 60
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 3
Enter key of the element to be deleted: 4
Element Deleted
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 2
Enter key of the element to be searched: 4
No element found at key 4
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 2
Enter key of the element to be searched: 2
Element at key 2 : 24
 
----------------------
Operations on Hash Table
 
----------------------
1.Insert element into the table
2.Search element from the key
3.Delete element at a key
4.Exit
Enter your choice: 4
 
 
------------------
(program exited with code: 1)
Press return to continue