hashTable.c

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

struct data
{
	int key;
	int value;
};

struct data *array;
int capacity = 10;
int size = 0;

/* this function gives a unique hash code to the given key */
int hashcode(int key)
{
	return (key % capacity);
}

/* it returns prime number just greater than array capacity */
int get_prime(int n)
{
	if (n % 2 == 0)
        {
		n++;
	}
	for (; !if_prime(n); n += 2);

	return n;
}

/* to check if given input (i.e n) is prime or not */
int if_prime(int n)
{
	int i;
	if ( n == 1  ||  n == 0)
        {
		return 0;
	}
	for (i = 2; i < n; i++)
        {
		if (n % i == 0)
                {
			return 0;
		}
	}
	return 1;
}

void init_array()
{
	int i;
	capacity = get_prime(capacity);
	array = (struct data*) malloc(capacity * sizeof(struct data));
	for (i = 0; i < capacity; i++)
        {
		array[i].key = 0;
		array[i].value = 0;
	}
}

/* to insert a key in the hash table */
void insert(int key)
{
	int index = hashcode(key);
	if (array[index].value == 0)
        {
		/*  key not present, insert it  */
		array[index].key = key;
		array[index].value = 1;
		size++;
		printf("\n Key (%d) has been inserted \n", key);
	}
	else if(array[index].key == key)
        {
		/*  updating already existing key  */
		printf("\n The key (%d) already present, hence updating its value \n", key);
		array[index].value += 1;
	}
	else
        {
		/*  key cannot be insert as the index is already containing some other key  */
		printf("\n ELEMENT CANNOT BE INSERTED \n");
	}
}

/* to remove a key from hash table */
void remove_element(int key)
{
	int index  = hashcode(key);
	if(array[index].value == 0)
        {
		printf("\n This key does not exist \n");
	}
	else {
		array[index].key = 0;
		array[index].value = 0;
		size--;
		printf("\n Key (%d) has been removed \n", key);
	}
}

/* to display all the elements of a hash table */
void display()
{
	int i;
	for (i = 0; i < capacity; i++)
        {
		if (array[i].value == 0)
                {
			printf("\n Array[%d] has no elements \n");
		}
		else
                {
			printf("\n array[%d] has elements -:\n key(%d) and value(%d) \t", i, array[i].key, array[i].value);
		}
	}
}

int size_of_hashtable()
{
	return size;
}

void main()
{
	int choice, key, value, n, c;

	init_array();

	do {
		printf("\n Implementation of Hash Table in C \n\n");
		printf("MENU-:  \n1.Inserting item in the Hash Table"
                               "\n2.Removing item from the Hash Table"
		               "\n3.Check the size of Hash Table"
                               "\n4.Display a Hash Table"
		       "\n\n Please enter your choice -:");

		scanf("%d", &choice);

		switch(choice)
                {
		case 1:
		      printf("Inserting element in Hash Table\n");
		      printf("Enter key -:\t");
		      scanf("%d", &key);
		      insert(key);
		      break;

		case 2:
		      printf("Deleting in Hash Table \n Enter the key to delete-:");
		      scanf("%d", &key);
		      remove_element(key);
		      break;

		case 3:
		      n = size_of_hashtable();
		      printf("Size of Hash Table is-:%d\n", n);
		      break;

		case 4:
		      display();
		      break;

		default:
		       printf("Wrong Input\n");

		}

		printf("\n Do you want to continue-:(press 1 for yes)\t");
		scanf("%d", &c);

	}while(c == 1);

}