Replace direct use of 0 with SetNull and IsNull

Replace x=0 with .SetNull(),
x==0 with IsNull(), x!=0 with !IsNull().
Replace uses of uint256(0) with uint256().

28 files changed, 68 insertions, 68 deletions

diff --git a/src/bitcoin-tx.cpp b/src/bitcoin-tx.cpp
index 05a85810ec..f095551c48 100644
--- a/src/bitcoin-tx.cpp
+++ b/src/bitcoin-tx.cpp
@@ -315,7 +315,7 @@ static bool findSighashFlags(int& flags, const string& flagStr)
 uint256 ParseHashUO(map<string,UniValue>& o, string strKey)
 {
     if (!o.count(strKey))
-        return 0;
+        return uint256();
     return ParseHashUV(o[strKey], strKey);
 }
 
@@ -485,7 +485,7 @@ static void MutateTx(CMutableTransaction& tx, const string& command,
 static void OutputTxJSON(const CTransaction& tx)
 {
     UniValue entry(UniValue::VOBJ);
-    TxToUniv(tx, 0, entry);
+    TxToUniv(tx, uint256(), entry);
 
     string jsonOutput = entry.write(4);
     fprintf(stdout, "%s\n", jsonOutput.c_str());
diff --git a/src/chain.h b/src/chain.h
index b459c975f8..d7741762c7 100644
--- a/src/chain.h
+++ b/src/chain.h
@@ -150,14 +150,14 @@ public:
         nFile = 0;
         nDataPos = 0;
         nUndoPos = 0;
-        nChainWork = 0;
+        nChainWork = uint256();
         nTx = 0;
         nChainTx = 0;
         nStatus = 0;
         nSequenceId = 0;
 
         nVersion       = 0;
-        hashMerkleRoot = 0;
+        hashMerkleRoot = uint256();
         nTime          = 0;
         nBits          = 0;
         nNonce         = 0;
@@ -282,11 +282,11 @@ public:
     uint256 hashPrev;
 
     CDiskBlockIndex() {
-        hashPrev = 0;
+        hashPrev = uint256();
     }
 
     explicit CDiskBlockIndex(const CBlockIndex* pindex) : CBlockIndex(*pindex) {
-        hashPrev = (pprev ? pprev->GetBlockHash() : 0);
+        hashPrev = (pprev ? pprev->GetBlockHash() : uint256());
     }
 
     ADD_SERIALIZE_METHODS;
diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index f4bc6e1d70..7e76a0bfa2 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -141,7 +141,7 @@ public:
         txNew.vout[0].nValue = 50 * COIN;
         txNew.vout[0].scriptPubKey = CScript() << ParseHex("04678afdb0fe5548271967f1a67130b7105cd6a828e03909a67962e0ea1f61deb649f6bc3f4cef38c4f35504e51ec112de5c384df7ba0b8d578a4c702b6bf11d5f") << OP_CHECKSIG;
         genesis.vtx.push_back(txNew);
-        genesis.hashPrevBlock = 0;
+        genesis.hashPrevBlock.SetNull();
         genesis.hashMerkleRoot = genesis.BuildMerkleTree();
         genesis.nVersion = 1;
         genesis.nTime    = 1231006505;
diff --git a/src/coins.cpp b/src/coins.cpp
index f4599ff39d..ef4f96fdee 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -42,7 +42,7 @@ bool CCoins::Spend(uint32_t nPos)
 
 bool CCoinsView::GetCoins(const uint256 &txid, CCoins &coins) const { return false; }
 bool CCoinsView::HaveCoins(const uint256 &txid) const { return false; }
-uint256 CCoinsView::GetBestBlock() const { return uint256(0); }
+uint256 CCoinsView::GetBestBlock() const { return uint256(); }
 bool CCoinsView::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return false; }
 bool CCoinsView::GetStats(CCoinsStats &stats) const { return false; }
 
@@ -57,7 +57,7 @@ bool CCoinsViewBacked::GetStats(CCoinsStats &stats) const { return base->GetStat
 
 CCoinsKeyHasher::CCoinsKeyHasher() : salt(GetRandHash()) {}
 
-CCoinsViewCache::CCoinsViewCache(CCoinsView *baseIn) : CCoinsViewBacked(baseIn), hasModifier(false), hashBlock(0) { }
+CCoinsViewCache::CCoinsViewCache(CCoinsView *baseIn) : CCoinsViewBacked(baseIn), hasModifier(false) { }
 
 CCoinsViewCache::~CCoinsViewCache()
 {
@@ -128,7 +128,7 @@ bool CCoinsViewCache::HaveCoins(const uint256 &txid) const {
 }
 
 uint256 CCoinsViewCache::GetBestBlock() const {
-    if (hashBlock == uint256(0))
+    if (hashBlock.IsNull())
         hashBlock = base->GetBestBlock();
     return hashBlock;
 }
diff --git a/src/coins.h b/src/coins.h
index 4f1afb00de..fe2eaa08e5 100644
--- a/src/coins.h
+++ b/src/coins.h
@@ -297,7 +297,7 @@ struct CCoinsStats
     uint256 hashSerialized;
     CAmount nTotalAmount;
 
-    CCoinsStats() : nHeight(0), hashBlock(0), nTransactions(0), nTransactionOutputs(0), nSerializedSize(0), hashSerialized(0), nTotalAmount(0) {}
+    CCoinsStats() : nHeight(0), nTransactions(0), nTransactionOutputs(0), nSerializedSize(0), nTotalAmount(0) {}
 };
 
 
diff --git a/src/core_write.cpp b/src/core_write.cpp
index b6fd7fe877..c3babec2fc 100644
--- a/src/core_write.cpp
+++ b/src/core_write.cpp
@@ -127,7 +127,7 @@ void TxToUniv(const CTransaction& tx, const uint256& hashBlock, UniValue& entry)
     }
     entry.pushKV("vout", vout);
 
-    if (hashBlock != 0)
+    if (!hashBlock.IsNull())
         entry.pushKV("blockhash", hashBlock.GetHex());
 
     entry.pushKV("hex", EncodeHexTx(tx)); // the hex-encoded transaction. used the name "hex" to be consistent with the verbose output of "getrawtransaction".
diff --git a/src/key.cpp b/src/key.cpp
index f09536fbbe..50ccb09213 100644
--- a/src/key.cpp
+++ b/src/key.cpp
@@ -84,7 +84,7 @@ bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig, uint32_
         nonce += test_case;
         int nSigLen = 72;
         int ret = secp256k1_ecdsa_sign((const unsigned char*)&hash, (unsigned char*)&vchSig[0], &nSigLen, begin(), (unsigned char*)&nonce);
-        nonce = 0;
+        nonce = uint256();
         if (ret) {
             vchSig.resize(nSigLen);
             return true;
@@ -116,7 +116,7 @@ bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig)
         uint256 nonce;
         prng.Generate((unsigned char*)&nonce, 32);
         int ret = secp256k1_ecdsa_sign_compact((const unsigned char*)&hash, &vchSig[1], begin(), (unsigned char*)&nonce, &rec);
-        nonce = 0;
+        nonce = uint256();
         if (ret)
             break;
     } while(true);
diff --git a/src/main.cpp b/src/main.cpp
index 4fcb4f093a..c392138ff3 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -261,7 +261,7 @@ struct CNodeState {
         nMisbehavior = 0;
         fShouldBan = false;
         pindexBestKnownBlock = NULL;
-        hashLastUnknownBlock = uint256(0);
+        hashLastUnknownBlock.SetNull();
         pindexLastCommonBlock = NULL;
         fSyncStarted = false;
         nStallingSince = 0;
@@ -349,12 +349,12 @@ void ProcessBlockAvailability(NodeId nodeid) {
     CNodeState *state = State(nodeid);
     assert(state != NULL);
 
-    if (state->hashLastUnknownBlock != 0) {
+    if (!state->hashLastUnknownBlock.IsNull()) {
         BlockMap::iterator itOld = mapBlockIndex.find(state->hashLastUnknownBlock);
         if (itOld != mapBlockIndex.end() && itOld->second->nChainWork > 0) {
             if (state->pindexBestKnownBlock == NULL || itOld->second->nChainWork >= state->pindexBestKnownBlock->nChainWork)
                 state->pindexBestKnownBlock = itOld->second;
-            state->hashLastUnknownBlock = uint256(0);
+            state->hashLastUnknownBlock.SetNull();
         }
     }
 }
@@ -1712,7 +1712,7 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
         return false;
 
     // verify that the view's current state corresponds to the previous block
-    uint256 hashPrevBlock = pindex->pprev == NULL ? uint256(0) : pindex->pprev->GetBlockHash();
+    uint256 hashPrevBlock = pindex->pprev == NULL ? uint256() : pindex->pprev->GetBlockHash();
     assert(hashPrevBlock == view.GetBestBlock());
 
     // Special case for the genesis block, skipping connection of its transactions
@@ -2835,7 +2835,7 @@ boost::filesystem::path GetBlockPosFilename(const CDiskBlockPos &pos, const char
 
 CBlockIndex * InsertBlockIndex(uint256 hash)
 {
-    if (hash == 0)
+    if (hash.IsNull())
         return NULL;
 
     // Return existing
@@ -3369,7 +3369,7 @@ void static ProcessGetData(CNode* pfrom)
                         vector<CInv> vInv;
                         vInv.push_back(CInv(MSG_BLOCK, chainActive.Tip()->GetBlockHash()));
                         pfrom->PushMessage("inv", vInv);
-                        pfrom->hashContinue = 0;
+                        pfrom->hashContinue.SetNull();
                     }
                 }
             }
@@ -3604,7 +3604,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
                     // Use deterministic randomness to send to the same nodes for 24 hours
                     // at a time so the setAddrKnowns of the chosen nodes prevent repeats
                     static uint256 hashSalt;
-                    if (hashSalt == 0)
+                    if (hashSalt.IsNull())
                         hashSalt = GetRandHash();
                     uint64_t hashAddr = addr.GetHash();
                     uint256 hashRand = hashSalt ^ (hashAddr<<32) ^ ((GetTime()+hashAddr)/(24*60*60));
@@ -3738,7 +3738,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         if (pindex)
             pindex = chainActive.Next(pindex);
         int nLimit = 500;
-        LogPrint("net", "getblocks %d to %s limit %d from peer=%d\n", (pindex ? pindex->nHeight : -1), hashStop==uint256(0) ? "end" : hashStop.ToString(), nLimit, pfrom->id);
+        LogPrint("net", "getblocks %d to %s limit %d from peer=%d\n", (pindex ? pindex->nHeight : -1), hashStop.IsNull() ? "end" : hashStop.ToString(), nLimit, pfrom->id);
         for (; pindex; pindex = chainActive.Next(pindex))
         {
             if (pindex->GetBlockHash() == hashStop)
@@ -3954,7 +3954,7 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
             // TODO: optimize: if pindexLast is an ancestor of chainActive.Tip or pindexBestHeader, continue
             // from there instead.
             LogPrint("net", "more getheaders (%d) to end to peer=%d (startheight:%d)\n", pindexLast->nHeight, pfrom->id, pfrom->nStartingHeight);
-            pfrom->PushMessage("getheaders", chainActive.GetLocator(pindexLast), uint256(0));
+            pfrom->PushMessage("getheaders", chainActive.GetLocator(pindexLast), uint256());
         }
     }
 
@@ -4452,7 +4452,7 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                 nSyncStarted++;
                 CBlockIndex *pindexStart = pindexBestHeader->pprev ? pindexBestHeader->pprev : pindexBestHeader;
                 LogPrint("net", "initial getheaders (%d) to peer=%d (startheight:%d)\n", pindexStart->nHeight, pto->id, pto->nStartingHeight);
-                pto->PushMessage("getheaders", chainActive.GetLocator(pindexStart), uint256(0));
+                pto->PushMessage("getheaders", chainActive.GetLocator(pindexStart), uint256());
             }
         }
 
@@ -4483,7 +4483,7 @@ bool SendMessages(CNode* pto, bool fSendTrickle)
                 {
                     // 1/4 of tx invs blast to all immediately
                     static uint256 hashSalt;
-                    if (hashSalt == 0)
+                    if (hashSalt.IsNull())
                         hashSalt = GetRandHash();
                     uint256 hashRand = inv.hash ^ hashSalt;
                     hashRand = Hash(BEGIN(hashRand), END(hashRand));
diff --git a/src/merkleblock.cpp b/src/merkleblock.cpp
index f9006d46d5..b51b002b95 100644
--- a/src/merkleblock.cpp
+++ b/src/merkleblock.cpp
@@ -76,7 +76,7 @@ uint256 CPartialMerkleTree::TraverseAndExtract(int height, unsigned int pos, uns
     if (nBitsUsed >= vBits.size()) {
         // overflowed the bits array - failure
         fBad = true;
-        return 0;
+        return uint256();
     }
     bool fParentOfMatch = vBits[nBitsUsed++];
     if (height==0 || !fParentOfMatch) {
@@ -84,7 +84,7 @@ uint256 CPartialMerkleTree::TraverseAndExtract(int height, unsigned int pos, uns
         if (nHashUsed >= vHash.size()) {
             // overflowed the hash array - failure
             fBad = true;
-            return 0;
+            return uint256();
         }
         const uint256 &hash = vHash[nHashUsed++];
         if (height==0 && fParentOfMatch) // in case of height 0, we have a matched txid
@@ -128,16 +128,16 @@ uint256 CPartialMerkleTree::ExtractMatches(std::vector<uint256> &vMatch) {
     vMatch.clear();
     // An empty set will not work
     if (nTransactions == 0)
-        return 0;
+        return uint256();
     // check for excessively high numbers of transactions
     if (nTransactions > MAX_BLOCK_SIZE / 60) // 60 is the lower bound for the size of a serialized CTransaction
-        return 0;
+        return uint256();
     // there can never be more hashes provided than one for every txid
     if (vHash.size() > nTransactions)
-        return 0;
+        return uint256();
     // there must be at least one bit per node in the partial tree, and at least one node per hash
     if (vBits.size() < vHash.size())
-        return 0;
+        return uint256();
     // calculate height of tree
     int nHeight = 0;
     while (CalcTreeWidth(nHeight) > 1)
@@ -147,12 +147,12 @@ uint256 CPartialMerkleTree::ExtractMatches(std::vector<uint256> &vMatch) {
     uint256 hashMerkleRoot = TraverseAndExtract(nHeight, 0, nBitsUsed, nHashUsed, vMatch);
     // verify that no problems occured during the tree traversal
     if (fBad)
-        return 0;
+        return uint256();
     // verify that all bits were consumed (except for the padding caused by serializing it as a byte sequence)
     if ((nBitsUsed+7)/8 != (vBits.size()+7)/8)
-        return 0;
+        return uint256();
     // verify that all hashes were consumed
     if (nHashUsed != vHash.size())
-        return 0;
+        return uint256();
     return hashMerkleRoot;
 }
diff --git a/src/net.cpp b/src/net.cpp
index 6401ecbf83..0548468714 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -1949,7 +1949,7 @@ CNode::CNode(SOCKET hSocketIn, CAddress addrIn, std::string addrNameIn, bool fIn
     nRefCount = 0;
     nSendSize = 0;
     nSendOffset = 0;
-    hashContinue = 0;
+    hashContinue = uint256();
     nStartingHeight = -1;
     fGetAddr = false;
     fRelayTxes = false;
diff --git a/src/primitives/block.cpp b/src/primitives/block.cpp
index 2b6a302ee9..3b4a360395 100644
--- a/src/primitives/block.cpp
+++ b/src/primitives/block.cpp
@@ -74,7 +74,7 @@ uint256 CBlock::BuildMerkleTree(bool* fMutated) const
     if (fMutated) {
         *fMutated = mutated;
     }
-    return (vMerkleTree.empty() ? 0 : vMerkleTree.back());
+    return (vMerkleTree.empty() ? uint256() : vMerkleTree.back());
 }
 
 std::vector<uint256> CBlock::GetMerkleBranch(int nIndex) const
@@ -96,7 +96,7 @@ std::vector<uint256> CBlock::GetMerkleBranch(int nIndex) const
 uint256 CBlock::CheckMerkleBranch(uint256 hash, const std::vector<uint256>& vMerkleBranch, int nIndex)
 {
     if (nIndex == -1)
-        return 0;
+        return uint256();
     for (std::vector<uint256>::const_iterator it(vMerkleBranch.begin()); it != vMerkleBranch.end(); ++it)
     {
         if (nIndex & 1)
diff --git a/src/primitives/block.h b/src/primitives/block.h
index 1449882bd0..53fcd104ad 100644
--- a/src/primitives/block.h
+++ b/src/primitives/block.h
@@ -53,8 +53,8 @@ public:
     void SetNull()
     {
         nVersion = CBlockHeader::CURRENT_VERSION;
-        hashPrevBlock = 0;
-        hashMerkleRoot = 0;
+        hashPrevBlock.SetNull();
+        hashMerkleRoot.SetNull();
         nTime = 0;
         nBits = 0;
         nNonce = 0;
diff --git a/src/primitives/transaction.cpp b/src/primitives/transaction.cpp
index 230aedd896..848d4d3e60 100644
--- a/src/primitives/transaction.cpp
+++ b/src/primitives/transaction.cpp
@@ -72,7 +72,7 @@ void CTransaction::UpdateHash() const
     *const_cast<uint256*>(&hash) = SerializeHash(*this);
 }
 
-CTransaction::CTransaction() : hash(0), nVersion(CTransaction::CURRENT_VERSION), vin(), vout(), nLockTime(0) { }
+CTransaction::CTransaction() : nVersion(CTransaction::CURRENT_VERSION), vin(), vout(), nLockTime(0) { }
 
 CTransaction::CTransaction(const CMutableTransaction &tx) : nVersion(tx.nVersion), vin(tx.vin), vout(tx.vout), nLockTime(tx.nLockTime) {
     UpdateHash();
diff --git a/src/primitives/transaction.h b/src/primitives/transaction.h
index da35012300..1b5a47e0da 100644
--- a/src/primitives/transaction.h
+++ b/src/primitives/transaction.h
@@ -28,8 +28,8 @@ public:
         READWRITE(FLATDATA(*this));
     }
 
-    void SetNull() { hash = 0; n = (uint32_t) -1; }
-    bool IsNull() const { return (hash == 0 && n == (uint32_t) -1); }
+    void SetNull() { hash.SetNull(); n = (uint32_t) -1; }
+    bool IsNull() const { return (hash.IsNull() && n == (uint32_t) -1); }
 
     friend bool operator<(const COutPoint& a, const COutPoint& b)
     {
diff --git a/src/protocol.cpp b/src/protocol.cpp
index 71c6bd152b..2dfded43be 100644
--- a/src/protocol.cpp
+++ b/src/protocol.cpp
@@ -96,7 +96,7 @@ void CAddress::Init()
 CInv::CInv()
 {
     type = 0;
-    hash = 0;
+    hash.SetNull();
 }
 
 CInv::CInv(int typeIn, const uint256& hashIn)
diff --git a/src/pubkey.h b/src/pubkey.h
index 69b73a4e1c..b0768d4f47 100644
--- a/src/pubkey.h
+++ b/src/pubkey.h
@@ -27,7 +27,7 @@
 class CKeyID : public uint160
 {
 public:
-    CKeyID() : uint160(0) {}
+    CKeyID() : uint160() {}
     CKeyID(const uint160& in) : uint160(in) {}
 };
 
diff --git a/src/rest.cpp b/src/rest.cpp
index 4702f0d707..1ee1d52912 100644
--- a/src/rest.cpp
+++ b/src/rest.cpp
@@ -240,7 +240,7 @@ static bool rest_tx(AcceptedConnection* conn,
         throw RESTERR(HTTP_BAD_REQUEST, "Invalid hash: " + hashStr);
 
     CTransaction tx;
-    uint256 hashBlock = 0;
+    uint256 hashBlock = uint256();
     if (!GetTransaction(hash, tx, hashBlock, true))
         throw RESTERR(HTTP_NOT_FOUND, hashStr + " not found");
 
diff --git a/src/rpcblockchain.cpp b/src/rpcblockchain.cpp
index 71fb7c8233..4705c07b8c 100644
--- a/src/rpcblockchain.cpp
+++ b/src/rpcblockchain.cpp
@@ -70,7 +70,7 @@ Object blockToJSON(const CBlock& block, const CBlockIndex* blockindex, bool txDe
         if(txDetails)
         {
             Object objTx;
-            TxToJSON(tx, uint256(0), objTx);
+            TxToJSON(tx, uint256(), objTx);
             txs.push_back(objTx);
         }
         else
diff --git a/src/rpcrawtransaction.cpp b/src/rpcrawtransaction.cpp
index b87a8baac3..10dc2ca93e 100644
--- a/src/rpcrawtransaction.cpp
+++ b/src/rpcrawtransaction.cpp
@@ -89,7 +89,7 @@ void TxToJSON(const CTransaction& tx, const uint256 hashBlock, Object& entry)
     }
     entry.push_back(Pair("vout", vout));
 
-    if (hashBlock != 0) {
+    if (!hashBlock.IsNull()) {
         entry.push_back(Pair("blockhash", hashBlock.GetHex()));
         BlockMap::iterator mi = mapBlockIndex.find(hashBlock);
         if (mi != mapBlockIndex.end() && (*mi).second) {
@@ -178,7 +178,7 @@ Value getrawtransaction(const Array& params, bool fHelp)
         fVerbose = (params[1].get_int() != 0);
 
     CTransaction tx;
-    uint256 hashBlock = 0;
+    uint256 hashBlock;
     if (!GetTransaction(hash, tx, hashBlock, true))
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "No information available about transaction");
 
@@ -438,7 +438,7 @@ Value decoderawtransaction(const Array& params, bool fHelp)
         throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
 
     Object result;
-    TxToJSON(tx, 0, result);
+    TxToJSON(tx, uint256(), result);
 
     return result;
 }
diff --git a/src/rpcwallet.cpp b/src/rpcwallet.cpp
index af7e8221cc..21f6bcae3d 100644
--- a/src/rpcwallet.cpp
+++ b/src/rpcwallet.cpp
@@ -1477,7 +1477,7 @@ Value listsinceblock(const Array& params, bool fHelp)
 
     if (params.size() > 0)
     {
-        uint256 blockId = 0;
+        uint256 blockId;
 
         blockId.SetHex(params[0].get_str());
         BlockMap::iterator it = mapBlockIndex.find(blockId);
@@ -1510,7 +1510,7 @@ Value listsinceblock(const Array& params, bool fHelp)
     }
 
     CBlockIndex *pblockLast = chainActive[chainActive.Height() + 1 - target_confirms];
-    uint256 lastblock = pblockLast ? pblockLast->GetBlockHash() : 0;
+    uint256 lastblock = pblockLast ? pblockLast->GetBlockHash() : uint256();
 
     Object ret;
     ret.push_back(Pair("transactions", transactions));
diff --git a/src/script/standard.h b/src/script/standard.h
index 1d29ef57aa..dbeeace4d9 100644
--- a/src/script/standard.h
+++ b/src/script/standard.h
@@ -20,7 +20,7 @@ class CScript;
 class CScriptID : public uint160
 {
 public:
-    CScriptID() : uint160(0) {}
+    CScriptID() : uint160() {}
     CScriptID(const CScript& in);
     CScriptID(const uint160& in) : uint160(in) {}
 };
diff --git a/src/test/pmt_tests.cpp b/src/test/pmt_tests.cpp
index 56e0541664..af3d90f2eb 100644
--- a/src/test/pmt_tests.cpp
+++ b/src/test/pmt_tests.cpp
@@ -46,7 +46,7 @@ BOOST_AUTO_TEST_CASE(pmt_test1)
 
         // calculate actual merkle root and height
         uint256 merkleRoot1 = block.BuildMerkleTree();
-        std::vector<uint256> vTxid(nTx, 0);
+        std::vector<uint256> vTxid(nTx, uint256());
         for (unsigned int j=0; j<nTx; j++)
             vTxid[j] = block.vtx[j].GetHash();
         int nHeight = 1, nTx_ = nTx;
@@ -88,7 +88,7 @@ BOOST_AUTO_TEST_CASE(pmt_test1)
 
             // check that it has the same merkle root as the original, and a valid one
             BOOST_CHECK(merkleRoot1 == merkleRoot2);
-            BOOST_CHECK(merkleRoot2 != 0);
+            BOOST_CHECK(!merkleRoot2.IsNull());
 
             // check that it contains the matched transactions (in the same order!)
             BOOST_CHECK(vMatchTxid1 == vMatchTxid2);
@@ -112,7 +112,7 @@ BOOST_AUTO_TEST_CASE(pmt_malleability)
 
     CPartialMerkleTree tree(vTxid, vMatch);
     std::vector<uint256> vTxid2;
-    BOOST_CHECK(tree.ExtractMatches(vTxid) == 0);
+    BOOST_CHECK(tree.ExtractMatches(vTxid).IsNull());
 }
 
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/test/script_P2SH_tests.cpp b/src/test/script_P2SH_tests.cpp
index 63553556ec..77e70022df 100644
--- a/src/test/script_P2SH_tests.cpp
+++ b/src/test/script_P2SH_tests.cpp
@@ -210,7 +210,7 @@ BOOST_AUTO_TEST_CASE(set)
 BOOST_AUTO_TEST_CASE(is)
 {
     // Test CScript::IsPayToScriptHash()
-    uint160 dummy(0);
+    uint160 dummy;
     CScript p2sh;
     p2sh << OP_HASH160 << ToByteVector(dummy) << OP_EQUAL;
     BOOST_CHECK(p2sh.IsPayToScriptHash());
diff --git a/src/test/sigopcount_tests.cpp b/src/test/sigopcount_tests.cpp
index 3326601492..3c8264d89d 100644
--- a/src/test/sigopcount_tests.cpp
+++ b/src/test/sigopcount_tests.cpp
@@ -32,7 +32,7 @@ BOOST_AUTO_TEST_CASE(GetSigOpCount)
     BOOST_CHECK_EQUAL(s1.GetSigOpCount(false), 0U);
     BOOST_CHECK_EQUAL(s1.GetSigOpCount(true), 0U);
 
-    uint160 dummy(0);
+    uint160 dummy;
     s1 << OP_1 << ToByteVector(dummy) << ToByteVector(dummy) << OP_2 << OP_CHECKMULTISIG;
     BOOST_CHECK_EQUAL(s1.GetSigOpCount(true), 2U);
     s1 << OP_IF << OP_CHECKSIG << OP_ENDIF;
diff --git a/src/txdb.cpp b/src/txdb.cpp
index 5096ab19a5..4467cdce70 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -39,7 +39,7 @@ bool CCoinsViewDB::HaveCoins(const uint256 &txid) const {
 uint256 CCoinsViewDB::GetBestBlock() const {
     uint256 hashBestChain;
     if (!db.Read('B', hashBestChain))
-        return uint256(0);
+        return uint256();
     return hashBestChain;
 }
 
@@ -56,7 +56,7 @@ bool CCoinsViewDB::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) {
         CCoinsMap::iterator itOld = it++;
         mapCoins.erase(itOld);
     }
-    if (hashBlock != uint256(0))
+    if (!hashBlock.IsNull())
         BatchWriteHashBestChain(batch, hashBlock);
 
     LogPrint("coindb", "Committing %u changed transactions (out of %u) to coin database...\n", (unsigned int)changed, (unsigned int)count);
@@ -179,7 +179,7 @@ bool CBlockTreeDB::LoadBlockIndexGuts()
     boost::scoped_ptr<leveldb::Iterator> pcursor(NewIterator());
 
     CDataStream ssKeySet(SER_DISK, CLIENT_VERSION);
-    ssKeySet << make_pair('b', uint256(0));
+    ssKeySet << make_pair('b', uint256());
     pcursor->Seek(ssKeySet.str());
 
     // Load mapBlockIndex
diff --git a/src/wallet.cpp b/src/wallet.cpp
index 4920cb21fc..6c5af3bdc7 100644
--- a/src/wallet.cpp
+++ b/src/wallet.cpp
@@ -579,7 +579,7 @@ bool CWallet::AddToWallet(const CWalletTx& wtxIn, bool fFromLoadWallet)
             wtx.nOrderPos = IncOrderPosNext();
 
             wtx.nTimeSmart = wtx.nTimeReceived;
-            if (wtxIn.hashBlock != 0)
+            if (!wtxIn.hashBlock.IsNull())
             {
                 if (mapBlockIndex.count(wtxIn.hashBlock))
                 {
@@ -630,7 +630,7 @@ bool CWallet::AddToWallet(const CWalletTx& wtxIn, bool fFromLoadWallet)
         if (!fInsertedNew)
         {
             // Merge
-            if (wtxIn.hashBlock != 0 && wtxIn.hashBlock != wtx.hashBlock)
+            if (!wtxIn.hashBlock.IsNull() && wtxIn.hashBlock != wtx.hashBlock)
             {
                 wtx.hashBlock = wtxIn.hashBlock;
                 fUpdated = true;
@@ -795,7 +795,7 @@ int CWalletTx::GetRequestCount() const
         if (IsCoinBase())
         {
             // Generated block
-            if (hashBlock != 0)
+            if (!hashBlock.IsNull())
             {
                 map<uint256, int>::const_iterator mi = pwallet->mapRequestCount.find(hashBlock);
                 if (mi != pwallet->mapRequestCount.end())
@@ -811,7 +811,7 @@ int CWalletTx::GetRequestCount() const
                 nRequests = (*mi).second;
 
                 // How about the block it's in?
-                if (nRequests == 0 && hashBlock != 0)
+                if (nRequests == 0 && !hashBlock.IsNull())
                 {
                     map<uint256, int>::const_iterator mi = pwallet->mapRequestCount.find(hashBlock);
                     if (mi != pwallet->mapRequestCount.end())
@@ -2317,7 +2317,7 @@ int CMerkleTx::SetMerkleBranch(const CBlock& block)
 
 int CMerkleTx::GetDepthInMainChainINTERNAL(const CBlockIndex* &pindexRet) const
 {
-    if (hashBlock == 0 || nIndex == -1)
+    if (hashBlock.IsNull() || nIndex == -1)
         return 0;
     AssertLockHeld(cs_main);
 
diff --git a/src/wallet.h b/src/wallet.h
index 4d95d0ae2e..1d0dc97c6c 100644
--- a/src/wallet.h
+++ b/src/wallet.h
@@ -519,7 +519,7 @@ public:
 
     void Init()
     {
-        hashBlock = 0;
+        hashBlock = uint256();
         nIndex = -1;
         fMerkleVerified = false;
     }
diff --git a/src/walletdb.cpp b/src/walletdb.cpp
index 4fd7eb512b..0ec83e7b32 100644
--- a/src/walletdb.cpp
+++ b/src/walletdb.cpp
@@ -439,7 +439,7 @@ ReadKeyValue(CWallet* pwallet, CDataStream& ssKey, CDataStream& ssValue,
             }
             CKey key;
             CPrivKey pkey;
-            uint256 hash = 0;
+            uint256 hash;
 
             if (strType == "key")
             {
@@ -464,7 +464,7 @@ ReadKeyValue(CWallet* pwallet, CDataStream& ssKey, CDataStream& ssValue,
 
             bool fSkipCheck = false;
 
-            if (hash != 0)
+            if (!hash.IsNull())
             {
                 // hash pubkey/privkey to accelerate wallet load
                 std::vector<unsigned char> vchKey;