implemented first draft of addToTree

bintree.c

@@ -1,3 +1,4 @@
+#include <stdlib.h>
 #include <string.h>
 #include "stack.h"
 #include "bintree.h"
@@ -12,7 +13,42 @@
 // if isDuplicate is NULL, otherwise ignores duplicates and sets isDuplicate to 1 (or to 0 if a new entry is added).
 TreeNode *addToTree(TreeNode *root, const void *data, size_t dataSize, CompareFctType compareFct, int *isDuplicate)
 {
+    if (root == NULL) {
+        TreeNode *newNode = (TreeNode *)malloc(sizeof(TreeNode));
+        if (newNode == NULL) {
+            return NULL;
+        }
 
+        newNode->data = malloc(dataSize);
+        if (newNode->data == NULL) {
+            free(newNode);
+            return NULL;
+        }
+        memcpy(newNode->data, data, dataSize);
+        newNode->left = NULL;
+        newNode->right = NULL;
+
+        if (isDuplicate != NULL) {
+            *isDuplicate = 0;
+        }
+        return newNode;
+    }
+
+    int cmp = compareFct(data, root->data);
+
+    if (cmp == 0 && isDuplicate != NULL) {
+        *isDuplicate = 1;
+        return root;
+    }
+
+    if (cmp < 0) {
+        root->left = addToTree(root->left, data, dataSize, compareFct, isDuplicate);
+    } else {
+        /* Insert duplicates on the right side if they are allowed (isDuplicate == NULL). */
+        root->right = addToTree(root->right, data, dataSize, compareFct, isDuplicate);
+    }
+
+    return root;
 }
 
 // Iterates over the tree given by root. Follows the usage of strtok. If tree is NULL, the next entry of the last tree given is returned in ordering direction.