Hash table done in C

hashtable.c

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

#include "hashtable.h"

struct nlist *hashtab[HASHSIZE];

unsigned hash(char *s) {
	unsigned hashval = 0;
	while(*s) hashval += *s++;
	return hashval % HASHSIZE;
}

struct nlist *lookup(char *key) {
	for (struct nlist *p = hashtab[hash(key)]; p != NULL; p = p->next)
		if(strcmp(key, p->key) == 0)
			return p;
	return NULL;
}

struct nlist *install(char* key, int value) {
	struct nlist *p;
	if ((p = lookup(key)) == NULL) {
		p = malloc(sizeof(struct nlist));
		unsigned hashval = hash(key);
		p->key = strdup(key);
		p->value = value;
		p->next = hashtab[hashval];
		hashtab[hashval] = p;
	} else {
		p->value = value;
	}
	return p;
}

hashtable.h

#ifndef _HASHTABLE_H_
#define _HASHTABLE_H_ TRUE


#define HASHSIZE 100

struct nlist {
	struct nlist *next;
	char* key;
	int value;
};

unsigned hash(char *s);
struct nlist *lookup(char *key);
struct nlist *install(char* key, int value);


#endif

table_demo.c

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

#include "hashtable.h"

int main(int argc, char const *argv[])
{
	install("aa", 5);
	install("aggarwal", 2);
	install("b", 7);
	struct nlist *n = lookup("b");
	assert (n->value == 7);
	return 0;
}