diff --git a/src/httprpc.cpp b/src/httprpc.cpp
--- a/src/httprpc.cpp
+++ b/src/httprpc.cpp
@@ -62,7 +62,7 @@
 };
 
 /* Stored RPC timer interface (for unregistration) */
-static HTTPRPCTimerInterface *httpRPCTimerInterface = 0;
+static HTTPRPCTimerInterface *httpRPCTimerInterface = nullptr;
 
 static void JSONErrorReply(HTTPRequest *req, const UniValue &objError,
                            const UniValue &id) {
@@ -408,6 +408,6 @@
     if (httpRPCTimerInterface) {
         RPCUnsetTimerInterface(httpRPCTimerInterface);
         delete httpRPCTimerInterface;
-        httpRPCTimerInterface = 0;
+        httpRPCTimerInterface = nullptr;
     }
 }
diff --git a/src/httpserver.cpp b/src/httpserver.cpp
--- a/src/httpserver.cpp
+++ b/src/httpserver.cpp
@@ -155,13 +155,13 @@
 /** HTTP module state */
 
 //! libevent event loop
-static struct event_base *eventBase = 0;
+static struct event_base *eventBase = nullptr;
 //! HTTP server
-struct evhttp *eventHTTP = 0;
+struct evhttp *eventHTTP = nullptr;
 //! List of subnets to allow RPC connections from
 static std::vector<CSubNet> rpc_allow_subnets;
 //! Work queue for handling longer requests off the event loop thread
-static WorkQueue<HTTPClosure> *workQueue = 0;
+static WorkQueue<HTTPClosure> *workQueue = nullptr;
 //! Handlers for (sub)paths
 std::vector<HTTPPathHandler> pathHandlers;
 //! Bound listening sockets
@@ -505,11 +505,11 @@
     }
     if (eventHTTP) {
         evhttp_free(eventHTTP);
-        eventHTTP = 0;
+        eventHTTP = nullptr;
     }
     if (eventBase) {
         event_base_free(eventBase);
-        eventBase = 0;
+        eventBase = nullptr;
     }
     LogPrint(BCLog::HTTP, "Stopped HTTP server\n");
 }
@@ -608,10 +608,10 @@
         new HTTPEvent(eventBase, true, std::bind(evhttp_send_reply, req,
                                                  nStatus, (const char *)nullptr,
                                                  (struct evbuffer *)nullptr));
-    ev->trigger(0);
+    ev->trigger(nullptr);
     replySent = true;
     // transferred back to main thread.
-    req = 0;
+    req = nullptr;
 }
 
 CService HTTPRequest::GetPeer() {
diff --git a/src/support/lockedpool.h b/src/support/lockedpool.h
--- a/src/support/lockedpool.h
+++ b/src/support/lockedpool.h
@@ -162,7 +162,7 @@
      * proceeds, but it could warn.
      */
     LockedPool(std::unique_ptr<LockedPageAllocator> allocator,
-               LockingFailed_Callback lf_cb_in = 0);
+               LockingFailed_Callback lf_cb_in = nullptr);
     ~LockedPool();
 
     /**
diff --git a/src/torcontrol.cpp b/src/torcontrol.cpp
--- a/src/torcontrol.cpp
+++ b/src/torcontrol.cpp
@@ -130,7 +130,7 @@
 };
 
 TorControlConnection::TorControlConnection(struct event_base *_base)
-    : base(_base), b_conn(0) {}
+    : base(_base), b_conn(nullptr) {}
 
 TorControlConnection::~TorControlConnection() {
     if (b_conn) {
@@ -246,7 +246,7 @@
     if (b_conn) {
         bufferevent_free(b_conn);
     }
-    b_conn = 0;
+    b_conn = nullptr;
     return true;
 }
 
@@ -468,7 +468,7 @@
 TorController::~TorController() {
     if (reconnect_ev) {
         event_free(reconnect_ev);
-        reconnect_ev = 0;
+        reconnect_ev = nullptr;
     }
     if (service.IsValid()) {
         RemoveLocal(service);
diff --git a/src/validation.h b/src/validation.h
--- a/src/validation.h
+++ b/src/validation.h
@@ -522,7 +522,7 @@
 
 public:
     CScriptCheck()
-        : amount(), ptxTo(0), nIn(0), nFlags(0), cacheStore(false),
+        : amount(), ptxTo(nullptr), nIn(0), nFlags(0), cacheStore(false),
           error(SCRIPT_ERR_UNKNOWN_ERROR), txdata() {}
 
     CScriptCheck(const CScript &scriptPubKeyIn, const Amount amountIn,
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -1890,11 +1890,11 @@
     for (CWallet::TxItems::const_reverse_iterator it = txOrdered.rbegin();
          it != txOrdered.rend(); ++it) {
         CWalletTx *const pwtx = (*it).second.first;
-        if (pwtx != 0) {
+        if (pwtx != nullptr) {
             ListTransactions(pwallet, *pwtx, strAccount, 0, true, ret, filter);
         }
         CAccountingEntry *const pacentry = (*it).second.second;
-        if (pacentry != 0) {
+        if (pacentry != nullptr) {
             AcentryToJSON(*pacentry, strAccount, ret);
         }
 
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -796,7 +796,7 @@
         CWalletTx *const pwtx = (*it).second.first;
         CAccountingEntry *const pacentry = (*it).second.second;
         int64_t &nOrderPos =
-            (pwtx != 0) ? pwtx->nOrderPos : pacentry->nOrderPos;
+            (pwtx != nullptr) ? pwtx->nOrderPos : pacentry->nOrderPos;
 
         if (nOrderPos == -1) {
             nOrderPos = nOrderPosNext++;
@@ -1875,7 +1875,7 @@
 }
 
 Amount CWalletTx::GetAvailableCredit(bool fUseCache) const {
-    if (pwallet == 0) {
+    if (pwallet == nullptr) {
         return Amount::zero();
     }
 
@@ -1922,7 +1922,7 @@
 }
 
 Amount CWalletTx::GetAvailableWatchOnlyCredit(const bool &fUseCache) const {
-    if (pwallet == 0) {
+    if (pwallet == nullptr) {
         return Amount::zero();
     }
 
diff --git a/src/wallet/walletdb.cpp b/src/wallet/walletdb.cpp
--- a/src/wallet/walletdb.cpp
+++ b/src/wallet/walletdb.cpp
@@ -634,8 +634,8 @@
     pwallet->laccentries.clear();
     ListAccountCreditDebit("*", pwallet->laccentries);
     for (CAccountingEntry &entry : pwallet->laccentries) {
-        pwallet->wtxOrdered.insert(std::make_pair(
-            entry.nOrderPos, CWallet::TxPair((CWalletTx *)0, &entry)));
+        pwallet->wtxOrdered.insert(
+            std::make_pair(entry.nOrderPos, CWallet::TxPair(nullptr, &entry)));
     }
 
     return result;
diff --git a/src/zmq/zmqabstractnotifier.h b/src/zmq/zmqabstractnotifier.h
--- a/src/zmq/zmqabstractnotifier.h
+++ b/src/zmq/zmqabstractnotifier.h
@@ -14,7 +14,7 @@
 
 class CZMQAbstractNotifier {
 public:
-    CZMQAbstractNotifier() : psocket(0) {}
+    CZMQAbstractNotifier() : psocket(nullptr) {}
     virtual ~CZMQAbstractNotifier();
 
     template <typename T> static CZMQAbstractNotifier *Create() {
diff --git a/src/zmq/zmqnotificationinterface.cpp b/src/zmq/zmqnotificationinterface.cpp
--- a/src/zmq/zmqnotificationinterface.cpp
+++ b/src/zmq/zmqnotificationinterface.cpp
@@ -112,7 +112,7 @@
         }
         zmq_ctx_destroy(pcontext);
 
-        pcontext = 0;
+        pcontext = nullptr;
     }
 }
 
diff --git a/src/zmq/zmqpublishnotifier.cpp b/src/zmq/zmqpublishnotifier.cpp
--- a/src/zmq/zmqpublishnotifier.cpp
+++ b/src/zmq/zmqpublishnotifier.cpp
@@ -116,7 +116,7 @@
         zmq_close(psocket);
     }
 
-    psocket = 0;
+    psocket = nullptr;
 }
 
 bool CZMQAbstractPublishNotifier::SendMessage(const char *command,
@@ -127,7 +127,7 @@
     uint8_t msgseq[sizeof(uint32_t)];
     WriteLE32(&msgseq[0], nSequence);
     int rc = zmq_send_multipart(psocket, command, strlen(command), data, size,
-                                msgseq, (size_t)sizeof(uint32_t), (void *)0);
+                                msgseq, (size_t)sizeof(uint32_t), nullptr);
     if (rc == -1) {
         return false;
     }