added a dictionary

I added a dictionary.

Data Structures/dictionary/README.md

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+## Dictionary 
+
+This is simple and generic dictionary. You can instantiate multiple dictionaries with
+the constructor. See interface below.
+
+Each dictionary has space for 1000 elements. 
+
+You need add the files **dic.c** and **dic.h** in your project directory.
+After that you include dic.h
+
+### Overview about functions
+
+``` c
+Dictionary * create_dict(void);
+```
+create_dict: is a simple constructor for creating 
+             a dictionary and setting up the 
+             member field 'number_of_elements'
+             and prepares the inner array 'elements'
+
+``` c
+int add_item_label(Dictionary *,char label[],void *);
+```
+add_item_label: adds item (void*) to the dictionary at given label 
+                returns 0 if adding was sucessful otherwise -1
+
+
+``` c
+int add_item_index(Dictionary *, int index, void *);
+```
+ add_item_index: adds item (void*) to the dictionary at given index (int) 
+                returns 0 if adding was sucessful otherwise -1
+
+``` c
+void * get_element_label(Dictionary *, char []);
+```
+get_element: returns the element at given label 
+
+
+``` c
+void * get_element_index(Dictionary *, int);
+```
+get_element: returns the element at given index 
+
+
+``` c
+void destroy(Dictionary *);
+```
+simple destructor function for avoiding memory leaks.

Data Structures/dictionary/dict.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include "dict.h"
+
+
+/* simple constructor */
+Dictionary * create_dict(void)
+{
+    Dictionary * p_dic = malloc(sizeof (Dictionary));
+    if (p_dic)
+    {
+        p_dic->number_of_elements = 0;
+
+        /* initializes the elemens of the array with NULL-pointer */
+        for (int i = 0; i < MAXELEMENTS; i++) 
+        {
+            p_dic->elements[i] = NULL;
+        }
+
+        return p_dic;
+    }
+    else 
+    {
+        printf("unable to create a dictionary\n");
+        return NULL;
+    }
+}
+
+
+/*
+    utility function
+    sdbm hash algorithm
+    returns a hashcode for the given string 's'
+*/
+int get_hash(char s[])
+{
+    unsigned int hash_code = 0;
+
+    /* iterates over string at each character */
+    for (int counter = 0; s[counter]!='\0'; counter++)
+    {
+        /* actual computing of the hash code */
+        hash_code = s[counter] + (hash_code << 6) + (hash_code << 16) - hash_code;
+    }
+
+    /* % modulo is for fitting the index in array. */
+    return hash_code % MAXELEMENTS;
+}
+
+
+int add_item_label(Dictionary * dic,char label[],void * item)
+{
+    unsigned int index = get_hash(label);
+
+    /* make sure index is fitting */
+    if (index < MAXELEMENTS)
+    {
+        dic->elements[index] = item;
+        return 0;
+    } 
+    
+    /* error case */
+    return -1; 
+}
+
+
+int add_item_index(Dictionary * dic , int index, void * item)
+{
+    /* make sure whether this place is already given */
+    if (!dic->elements[index])
+    {
+        dic->elements[index] = item;
+        return 0;
+    } 
+    
+    /* error case */
+    return -1;
+}
+
+
+void * get_element_label(Dictionary * dict, char s[])
+{
+    int index = get_hash(s);
+    if (dict->elements[index])
+    {
+        return dict->elements[index];
+    }
+
+    printf("None entry at given label\n");
+    return NULL;
+}
+
+
+void * get_element_index(Dictionary * dict, int index)
+{
+    if (index >= 0 && index < MAXELEMENTS)
+    {
+        return dict->elements[index];
+    }
+    
+    printf("index out of bounds!\n");
+    return NULL;
+}
+
+
+void destroy(Dictionary * dict)
+{
+    free(dict);
+}

Data Structures/dictionary/dict.h

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+/*
+    author: Christian Bender
+    public interface for the dictionary. 
+
+    The dictionary prepares space for 1000 elements.
+*/
+
+#ifndef __DICT__H
+#define __DICT__H
+
+#define MAXELEMENTS 1000
+
+/*
+    special data type called 'Dictionary'
+    for generic use
+*/
+typedef struct Dict 
+{
+    /* 
+        void* array for generic use of the dictionary.
+        there actual saves the entries.
+    */
+    void * elements[MAXELEMENTS];
+
+    /* contains the number of elements in this dictionary */
+    int number_of_elements;
+
+} Dictionary;
+
+/*
+    create_dict: is a simple constructor for creating 
+                a dictionary and setting up the 
+                member field 'number_of_elements'
+                and prepares the inner array 'elements'
+*/
+Dictionary * create_dict(void);
+
+/* 
+    add_item_label: adds item (void*) to the dictionary at given label 
+    returns 0 if adding was sucessful otherwise -1
+*/
+int add_item_label(Dictionary *,char label[],void *);
+
+/* 
+    add_item_index: adds item (void*) to the dictionary at given index (int) 
+    returns 0 if adding was sucessful otherwise -1
+*/
+int add_item_index(Dictionary *, int index, void *);
+
+
+/*
+    get_element: returns the element at given label 
+*/
+void * get_element_label(Dictionary *, char []);
+
+
+/*
+    get_element: returns the element at given index 
+*/
+void * get_element_index(Dictionary *, int );
+
+/* 
+    simple destrcutor function
+*/
+void destroy(Dictionary *);
+
+
+#endif

Data Structures/dictionary/test_program.c

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+/*
+    author: Christian Bender
+    This is a simple test program for the dictionary.
+*/
+
+#include <stdio.h>
+
+/* includes the dictionary */
+#include "dict.h"
+
+int main(void)
+{
+    Dictionary * testObj1;
+    Dictionary * testObj2;
+
+    int value = 28; 
+
+    testObj1 = create_dict();
+    testObj2 = create_dict();
+
+    add_item_label(testObj1,"age",&value);
+    add_item_label(testObj2,"name","Christian");
+   
+
+    /*
+        test for function add_item_label
+
+        attention: 
+        The void* pointer must be convert into an int* pointer. 
+        After that you can dereference it.
+    */
+    printf("My age is %d\n",*((int *)get_element_label(testObj1,"age")));
+    printf("My name is %s\n",get_element_label(testObj2,"name"));
+
+    /* test for function add_item_index */
+    if (!add_item_index(testObj1,0,&value))
+    {
+        printf("My age at index %d is %d\n",0,*((int *)get_element_index(testObj1,0)));
+    }
+
+    /* error scenario */
+    /* get_element_label(testObj,"none"); */
+
+    /* tidy up */
+    destroy(testObj1);
+    destroy(testObj2);
+
+    return 0;
+}