Add expression tree interface documentation and include guards

src/calculator_exptree.c

@@ -1,3 +1,6 @@
+// calculator_exptree.c
+// TODO: file description
+
 #include <bstrlib.h>
 #include <bstrlib_helper.h>
 #include "calculator_exptree.h"

src/includes/calculator_exptree.h

@@ -1,19 +1,55 @@
 // calculator_exptree.h
+// TODO: file description
 
-struct exptree_node; // fwd declaration
+#ifndef CALCULATOR_EXPTREE_H_INCLUDED
+#define CALCULATOR_EXPTREE_H_INCLUDED
+
+/**
+ * @brief Forward declaration of struct exptree_node
+ * 
+ */
+struct exptree_node;
 
 // cannot fwd declare CounterList because it was an anonymous struct (changed)
-// thus we named CounterList to avoid unnecessary cyclic inclusion dependency with:
+// thus we named CounterList to avoid unnecessary inclusion dependency with:
 // #include "perfgroup.h"
-struct CounterList; // fwd declaration
+/**
+ * @brief Forward declaration of struct CounterList
+ * 
+ */
+struct CounterList;
 
-// TODO: documentation of interfaces
 // TODO: do we want "print_expression_tree"?
 
+/**
+ * @brief Builds a binary expression tree from expression expr
+ * 
+ * @param expr The expression
+ * @return struct exptree_node* Expression tree node on success, NULL on error
+ */
 extern struct exptree_node *make_expression_tree(const char *expr);
 
+/**
+ * @brief Deallocates the binary expression tree
+ * 
+ * @param root The root node
+ */
 extern void free_expression_tree(struct exptree_node *root);
 
-extern double evaluate_expression_tree(const struct exptree_node *node, const struct CounterList *clist);
+/**
+ * @brief Evaluates the expression tree with values from counter list
+ * 
+ * @param root The root node
+ * @param clist The counter list
+ * @return double The value of the expression tree evaluation on success, NAN on error
+ */
+extern double evaluate_expression_tree(const struct exptree_node *root, const struct CounterList *clist);
 
+/**
+ * @brief Prints the expression tree in infix order
+ * 
+ * @param root The root node
+ */
 extern void print_expression_tree(const struct exptree_node *root);
+
+#endif /* CALCULATOR_EXPTREE_H_INCLUDED */