Insert function of Hashtable in C

Question

So, I have the functions. How can I insert numbers in the Hashtable ? A for that goes until the size of the table? I don't know what goes inside the for , if it is exists.

#include <stdio.h>

//Structure
typedef struct Element {
    int key;
    int value;
} Element;

typedef struct HashTable {
    Element *table[11];
} HashTable;


//Create an empty Hash
HashTable* createHashTable() {
    HashTable *Raking = malloc(sizeof(HashTable));

    int i;
    for (i = 0; i < 11; i++) {
        Raking->table[i] = NULL;
    }
    return Raking;
}

//Insert element
void insertElement(HashTable *Raking, int key, int value) {

    int h = hashFunction(key);

    while(Raking->table[h] != NULL) {

        if(Raking->table[h]->key == key) {
            Raking->table[h]->value = value;
            break;
        }

        h = (h + 1) % 11;
    }

    if(Raking->table[h] == NULL) {
        Element *newElement = (Element*) malloc(sizeof(Element));
        newElement->key = key;
        newElement->value = value;
        Raking->table[h] = newElement;
    }
}

int main() {

    HashTable * Ranking = createHashTable();


    /** ??? **/


}

Could someone explain to me how to write my main function with these structures? In this case I'm fixing the number of elements in this table, right? (table [11]) What could I do for the user to determine the size of the hash table? is it possible? Or should I set the size?

Answer 1

I've added comments and changes to your code that I feel will be of use to you. I've also adapted it so that size is not hardcoded. Finally I free all the malloc -ed statements.

This compiles without errors and I've tested it for memory leaks and other errors using valgrind and found no complaints.

Let me know if something is not clear and the comments fail to explain it. I've tried to stick to your code as much as possible but I've not had a chance to test the functionality properly.

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

//Structure
typedef struct Element {
    int key;
    int value;
} Element; /* you had a syntax error here */

typedef struct HashTable {
    int size; /* we will need the size for the traversal */
    Element *table; /* leave it as a pointer */
} HashTable; /* a syntax error here too */

HashTable* createHashTable(int size) {
    HashTable *Ranking = malloc(sizeof(HashTable));

    /* set the pointer to point to a dynamic array of size 'size' */
    /* this way you don't have to hardcode the size */
    Ranking->table = malloc(sizeof(Element) * size); 
    Ranking->size = size;

    /* initialisation is a bit different because we don't have pointers here */
    /* only table is a pointer, not its elements */
     int i;
     for (i = 0; i < size; i++) {
         Ranking->table[i].key = 0; 
         Ranking->table[i].value = 0;
     }

    return Ranking;
}

/* I implemented a fake hashFunction just to test the code */
/* all it does is make sure the key does not exceed the size of the table */
int hashFunction(int key, int size)
{
    return (key % size);
}

//Insert element
void insertElement(HashTable *Ranking, int key, int value) {

    int h = hashFunction(key, Ranking->size);
    int i = 0;

    /* if hash is full and key doesn't exist your previous loop would have gone on forever, I've added a check */
    /* also notice that I check if table[h] has empty key, not if it's null as this is not a pointer */
    while(Ranking->table[h].key != 0 && (i < Ranking->size)) {

        if(Ranking->table[h].key == key) {
            Ranking->table[h].value = value;
            return; /* break is intended to quit the loop, but actually we want to exit the function altogether */
        }

        h = (h + 1) % Ranking->size; /* changed 11 to the size specified */
        i++; /* advance the loop index */
    }

    /* okay found a free slot, store it there */
    if(Ranking->table[h].key == 0) {
        /* we now do direct assignment, no need for pointers */
        Ranking->table[h].key = key;
        Ranking->table[h].value = value;
    }
}

int main() {

    int size = 0;
    scanf(" %d", &size);

    HashTable *Ranking = createHashTable(size);

    insertElement(Ranking, 113, 10); /* this is just a test, 113 will be hashed to be less than size */

    /* we free everything we have malloc'ed */
    free(Ranking->table);
    free(Ranking);

    return 0;
}