fix forward declarations

hashing/double_hash_hash_table.cpp

@@ -15,8 +15,8 @@ namespace {  // keep the code local to this file by assigning them to an unnamed
 
 // fwd declarations
 using Entry = struct Entry;
-bool putProber(Entry entry, int key);
-bool searchingProber(Entry entry, int key);
+bool putProber(const Entry& entry, int key);
+bool searchingProber(const Entry& entry, int key);
 void add(int key);
 
 // Undocumented globals
@@ -112,7 +112,7 @@ int doubleHash(int key, bool searching) {
  * @returns `true` if key is not present or is a `toumb`
  * @returns `false` is already occupied
  */
-bool putProber(Entry entry, int key) {
+bool putProber(const Entry& entry, int key) {
     if (entry.key == notPresent || entry.key == tomb) {
         return true;
     }
@@ -125,7 +125,7 @@ bool putProber(Entry entry, int key) {
  * @returns `true` if found
  * @returns `false` if not found
  */
-bool searchingProber(Entry entry, int key) {
+bool searchingProber(const Entry& entry, int key) {
     if (entry.key == key) {
         return true;
     }

hashing/linear_probing_hash_table.cpp

@@ -18,15 +18,10 @@ using std::string;
 namespace {  // keep the code local to this file by assigning them to an unnamed
              // namespace
 
-/** Node object that holds key */
-struct Entry {
-    explicit Entry(int key = notPresent) : key(key) {}  ///< constructor
-    int key;                                            ///< key value
-};
-
 // fwd declarations
-bool putProber(Entry entry, int key);
-bool searchingProber(Entry entry, int key);
+using Entry = struct Entry;
+bool putProber(const Entry& entry, int key);
+bool searchingProber(const Entry& entry, int key);
 void add(int key);
 
 // Undocumented globals
@@ -37,6 +32,12 @@ int tomb = -1;
 int size;
 bool rehashing;
 
+/** Node object that holds key */
+struct Entry {
+    explicit Entry(int key = notPresent) : key(key) {}  ///< constructor
+    int key;                                            ///< key value
+};
+
 /**
  * @brief Hash a key. Uses the STL library's `std::hash()` function.
  *

hashing/quadratic_probing_hash_table.cpp

@@ -18,8 +18,8 @@ namespace {  // keep the code local to this file by assigning them to an unnamed
 
 // fwd declarations
 using Entry = struct Entry;
-bool putProber(Entry entry, int key);
-bool searchingProber(Entry entry, int key);
+bool putProber(const Entry& entry, int key);
+bool searchingProber(const Entry& entry, int key);
 void add(int key);
 
 // globals
@@ -87,7 +87,7 @@ int quadraticProbe(int key, bool searching) {
 }
 
 // Finds empty spot
-bool putProber(Entry entry, int key) {
+bool putProber(const Entry& entry, int key) {
     if (entry.key == notPresent || entry.key == tomb) {
         return true;
     }
@@ -95,7 +95,7 @@ bool putProber(Entry entry, int key) {
 }
 
 // Looks for a matching key
-bool searchingProber(Entry entry, int key) {
+bool searchingProber(const Entry& entry, int key) {
     if (entry.key == key) {
         return true;
     }