diff --git a/00_Enumerated-Lists/enumerate.cpp b/00_Enumerated-Lists/enumerate.cpp
new file mode 100644
index 0000000..479bb49
--- /dev/null
+++ b/00_Enumerated-Lists/enumerate.cpp
@@ -0,0 +1,16 @@
+#include <eosiolib/eosio.hpp>
+#include <eosiolib/print.h>
+
+using namespace eosio;
+using std::string;
+
+class enumerate : eosio::contract {
+	
+	private:
+		// Game status types
+		enum game_status: uint8_t  {
+			OPEN		= 0,
+			PAUSED		= 1,
+			CLOSED		= 2
+		};
+};
\ No newline at end of file
diff --git a/01_Hashes/checksum.cpp b/01_Hashes/checksum.cpp
index 1c73483..11d5e5b 100644
--- a/01_Hashes/checksum.cpp
+++ b/01_Hashes/checksum.cpp
@@ -6,18 +6,68 @@
 using namespace eosio;
 using std::string;
 
+template <typename CharT>
+
 class crypto : eosio::contract {
 
 	public:
 
 		using contract::contract;
 
+		/**
+		 * Hash
+		 * @desc Hashes a given input string and prints to console
+		 * @author Mitch Pierias <https://github.com/MitchPierias>
+		 * @param str <std::string> String to hash
+		 * @public
+		 */
 		void hash(const string& str) {
+			// Hash the given string
+			checksum256 hashed = create_hash(str);
+			// Convert output to hexadecimal string
+			string result = to_hex(hashed);
+			// Print result
+			print(result);
+		}
+
+	private:
+
+		/**
+		 * Hash String
+		 * @desc Digests a hash from the provided string
+		 * @author Mitch Pierias <https://github.com/MitchPierias>
+		 * @param str <std::string> String to hash
+		 * @return result <checksum256> Hash digest
+		 * @private
+		 */
+		checksum256 create_hash(const string& str) {
 			// Hash the string to a checksum
-			checksum256 sum{};
+			checksum256 result{};
 			sha256(const_cast<char*>(str.c_str()), str.size(), &sum);
-			// Print output
-			printhex(&sum, sizeof(sum));
+			// Return resulting digest
+			return result;
+		}
+
+		/**
+		 * Checksum to Hexadecimal String
+		 * @desc Converts the provided checksum of specified length to a hexadecimal string
+		 * @author Mitch Pierias <https://github.com/MitchPierias>
+		 * @param data <CharT> Checksum character set
+		 * @param length <uint32_t> Checksum size
+		 * @return result <std::string> Hexadecimal string
+		 * @private
+		 */
+		string to_hex(const CharT* data, uint32_t length) {
+			// Construct variables
+			string result;
+			const char* hex_chars = "0123456789abcdef";
+			uint8_t* c = (uint8_t*)data;
+			// Iterate bytes and build result
+			for (uint32_t i = 0; i < length; ++i) {
+				(result += hex_chars[(c[i] >> 4)]) += hex_chars[(c[i] & 0x0f)];
+			}
+			// Return string
+			return result;
 		}
 };
 
diff --git a/02_Singletons/singletons.cpp b/02_Singletons/singletons.cpp
index 8b9b003..562ca78 100644
--- a/02_Singletons/singletons.cpp
+++ b/02_Singletons/singletons.cpp
@@ -14,7 +14,10 @@ class singletons : eosio::contract {
 		explicit singletons(action_name self) : contract(self), config(_self, _self) {}
 		// @abi action
 		void setclosed(bool isClosed) {
-			config.set(Config{isClosed}, _self);
+			auto state = config.get();
+			state.closed = isClosed;
+			config.set(state, _self);
+			print(state.closed);
 		}
 		// @abi action
 		void getclosed() {
diff --git a/11_ABI-Extensions/abiext.cpp b/11_ABI-Extensions/abiext.cpp
new file mode 100644
index 0000000..1ce0c04
--- /dev/null
+++ b/11_ABI-Extensions/abiext.cpp
@@ -0,0 +1,19 @@
+extern "C" void apply(uint64_t receiver, uint64_t code, uint64_t action) {
+
+	auto self = receiver;
+
+	if (code == self || code == N(eosio.token)) {
+
+		if (action == N(transfer)) {
+			eosio_assert(code == N(eosio.token), "EOS required for transfer");
+		}
+
+		TYPE thiscontract(self);
+
+		switch (action) {
+			EOSIO_API(TYPE, MEMBERS)
+		}
+
+		// Prevent contract destructor from executing `eosio_exit(0);`
+	}
+}
\ No newline at end of file