diff --git a/src/cc/auction.cpp b/src/cc/auction.cpp
index 8265dfc45..7b5f106d0 100644
--- a/src/cc/auction.cpp
+++ b/src/cc/auction.cpp
@@ -164,7 +164,7 @@ std::string AuctionBid(uint64_t txfee,uint256 itemhash,int64_t amount)
         mtx.vout.push_back(CTxOut(nValue,CScript() << ParseHex(HexStr(mypk)) << OP_CHECKSIG));
         return(FinalizeCCTx(-1LL,cp,mtx,mypk,txfee,opret));
     } else fprintf(stderr,"cant find Auction inputs\n");
-    return(0);
+    return("");
 }
 
 std::string AuctionDeliver(uint64_t txfee,uint256 itemhash,uint256 bidtxid)
@@ -184,7 +184,7 @@ std::string AuctionDeliver(uint64_t txfee,uint256 itemhash,uint256 bidtxid)
         mtx.vout.push_back(CTxOut(nValue,CScript() << ParseHex(HexStr(mypk)) << OP_CHECKSIG));
         return(FinalizeCCTx(-1LL,cp,mtx,mypk,txfee,opret));
     } else fprintf(stderr,"cant find Auction inputs\n");
-    return(0);
+    return("");
 }
 
 std::string AuctionPost(uint64_t txfee,uint256 itemhash,int64_t minbid,char *title,char *description)
@@ -200,7 +200,7 @@ std::string AuctionPost(uint64_t txfee,uint256 itemhash,int64_t minbid,char *tit
         mtx.vout.push_back(MakeCC1vout(EVAL_AUCTION,funds,Auctionpk));
         return(FinalizeCCTx(0,cp,mtx,mypk,txfee,opret));
     }
-    return(0);
+    return("");
 }
 
 
diff --git a/src/cc/dice.cpp b/src/cc/dice.cpp
index e35f367f3..0dbad5cd6 100644
--- a/src/cc/dice.cpp
+++ b/src/cc/dice.cpp
@@ -805,11 +805,11 @@ std::string DiceCreateFunding(uint64_t txfee,char *planstr,int64_t funds,int64_t
     if ( funds < 0 || minbet < 0 || maxbet < 0 || maxodds < 1 || timeoutblocks < 0 || timeoutblocks > 1440 )
     {
         fprintf(stderr,"negative parameter error\n");
-        return(0);
+        return("");
     }
     memset(&zero,0,sizeof(zero));
     if ( (cp= Diceinit(fundingPubKey,zero,&C,planstr,txfee,mypk,dicepk,sbits,a,b,c,d)) == 0 )
-        return(0);
+        return("");
     if ( AddNormalinputs(mtx,mypk,funds+3*txfee,60) > 0 )
     {
         mtx.vout.push_back(MakeCC1vout(cp->evalcode,funds,dicepk));
@@ -818,7 +818,7 @@ std::string DiceCreateFunding(uint64_t txfee,char *planstr,int64_t funds,int64_t
         return(FinalizeCCTx(0,cp,mtx,mypk,txfee,EncodeDiceFundingOpRet('F',sbits,minbet,maxbet,maxodds,timeoutblocks)));
     }
     fprintf(stderr,"cant find enough inputs\n");
-    return(0);
+    return("");
 }
 
 std::string DiceAddfunding(uint64_t txfee,char *planstr,uint256 fundingtxid,int64_t amount)
@@ -827,10 +827,10 @@ std::string DiceAddfunding(uint64_t txfee,char *planstr,uint256 fundingtxid,int6
     if ( amount < 0 )
     {
         fprintf(stderr,"negative parameter error\n");
-        return(0);
+        return("");
     }
     if ( (cp= Diceinit(fundingPubKey,fundingtxid,&C,planstr,txfee,mypk,dicepk,sbits,minbet,maxbet,maxodds,timeoutblocks)) == 0 )
-        return(0);
+        return("");
     scriptPubKey = CScript() << ParseHex(HexStr(mypk)) << OP_CHECKSIG;
     if ( 0 )
     {
@@ -854,7 +854,7 @@ std::string DiceAddfunding(uint64_t txfee,char *planstr,uint256 fundingtxid,int6
             return(FinalizeCCTx(0,cp,mtx,mypk,txfee,EncodeDiceOpRet('E',sbits,fundingtxid,hentropy,zeroid)));
         } else fprintf(stderr,"cant find enough inputs\n");
     } else fprintf(stderr,"only fund creator can add more funds (entropy)\n");
-    return(0);
+    return("");
 }
 
 std::string DiceBet(uint64_t txfee,char *planstr,uint256 fundingtxid,int64_t bet,int32_t odds)
@@ -863,21 +863,21 @@ std::string DiceBet(uint64_t txfee,char *planstr,uint256 fundingtxid,int64_t bet
     if ( bet < 0 || odds < 1 )
     {
         fprintf(stderr,"negative parameter error\n");
-        return(0);
+        return("");
     }
     if ( (cp= Diceinit(fundingPubKey,fundingtxid,&C,planstr,txfee,mypk,dicepk,sbits,minbet,maxbet,maxodds,timeoutblocks)) == 0 )
-        return(0);
+        return("");
     if ( bet < minbet || bet > maxbet || odds > maxodds )
     {
         fprintf(stderr,"Dice plan %s illegal bet %.8f: minbet %.8f maxbet %.8f or odds %d vs max.%d\n",planstr,(double)bet/COIN,(double)minbet/COIN,(double)maxbet/COIN,(int32_t)odds,(int32_t)maxodds);
-        return(0);
+        return("");
     }
     if ( (funding= DicePlanFunds(entropyval,entropytxid,sbits,cp,dicepk,fundingtxid)) >= 2*bet*odds+txfee && entropyval != 0 )
     {
         if ( myIsutxo_spentinmempool(entropytxid,0) != 0 )
         {
             fprintf(stderr,"entropy txid is spent\n");
-            return(0);
+            return("");
         }
         mtx.vin.push_back(CTxIn(entropytxid,0,CScript()));
         if ( AddNormalinputs(mtx,mypk,bet+2*txfee+odds,60) > 0 )
@@ -892,7 +892,7 @@ std::string DiceBet(uint64_t txfee,char *planstr,uint256 fundingtxid,int64_t bet
     if ( entropyval == 0 && funding != 0 )
         fprintf(stderr,"cant find dice entropy inputs\n");
     else fprintf(stderr,"cant find dice inputs\n");
-    return(0);
+    return("");
 }
 
 std::string DiceBetFinish(int32_t *resultp,uint64_t txfee,char *planstr,uint256 fundingtxid,uint256 bettxid,int32_t winlosetimeout)
@@ -903,7 +903,7 @@ std::string DiceBetFinish(int32_t *resultp,uint64_t txfee,char *planstr,uint256
     if ( (cp= Diceinit(fundingPubKey,fundingtxid,&C,planstr,txfee,mypk,dicepk,sbits,minbet,maxbet,maxodds,timeoutblocks)) == 0 )
     {
         fprintf(stderr,"Diceinit error\n");
-        return("0");
+        return("");
     }
     fundingpk = DiceFundingPk(fundingPubKey);
     if ( winlosetimeout != 0 )
@@ -918,7 +918,7 @@ std::string DiceBetFinish(int32_t *resultp,uint64_t txfee,char *planstr,uint256
     if ( AddNormalinputs(mtx,mypk,txfee,1) == 0 )
     {
         fprintf(stderr,"no txfee inputs for win/lose\n");
-        return("0");
+        return("");
     }
     if ( GetTransaction(bettxid,betTx,hashBlock,false) != 0 && GetTransaction(betTx.vin[0].prevout.hash,entropyTx,hashBlock,false) != 0 )
     {
@@ -932,7 +932,7 @@ std::string DiceBetFinish(int32_t *resultp,uint64_t txfee,char *planstr,uint256
                 if ( myIsutxo_spentinmempool(bettxid,0) != 0 || myIsutxo_spentinmempool(bettxid,1) != 0 )
                 {
                     fprintf(stderr,"bettxid already spent\n");
-                    return("0");
+                    return("");
                 }
                 //fprintf(stderr,"iswin.%d matches\n",iswin);
                 mtx.vin.push_back(CTxIn(bettxid,0,CScript()));
@@ -942,7 +942,7 @@ std::string DiceBetFinish(int32_t *resultp,uint64_t txfee,char *planstr,uint256
                     funcid = 'T';
                     if ( DiceVerifyTimeout(betTx,timeoutblocks) == 0 ) // hasnt timed out yet
                     {
-                        return("0");
+                        return("");
                     }
                     else
                     {
@@ -958,7 +958,7 @@ std::string DiceBetFinish(int32_t *resultp,uint64_t txfee,char *planstr,uint256
                     if ( odds < 1 || odds > maxodds )
                     {
                         fprintf(stderr,"illegal odds.%d vs maxodds.%d\n",(int32_t)odds,(int32_t)maxodds);
-                        return("0");
+                        return("");
                     }
                     CCchange = betTx.vout[0].nValue;
                     fundsneeded = txfee + odds*betTx.vout[1].nValue;
@@ -973,7 +973,7 @@ std::string DiceBetFinish(int32_t *resultp,uint64_t txfee,char *planstr,uint256
                     else
                     {
                         fprintf(stderr,"not enough inputs for %.8f\n",(double)fundsneeded/COIN);
-                        return("0");
+                        return("");
                     }
                 }
                 else
@@ -994,12 +994,12 @@ std::string DiceBetFinish(int32_t *resultp,uint64_t txfee,char *planstr,uint256
         {
             *resultp = -1;
             fprintf(stderr,"iswin.%d winlosetimeout.%d\n",iswin,winlosetimeout);
-            return("0");
+            return("");
         }
     }
     *resultp = -1;
     fprintf(stderr,"couldnt find bettx or entropytx\n");
-    return("0");
+    return("");
 }
 
 double DiceStatus(uint64_t txfee,char *planstr,uint256 fundingtxid,uint256 bettxid)
diff --git a/src/cc/fsm.cpp b/src/cc/fsm.cpp
index 6141d8a4a..04c620e99 100644
--- a/src/cc/fsm.cpp
+++ b/src/cc/fsm.cpp
@@ -149,7 +149,7 @@ int64_t AddFSMInputs(struct CCcontract_info *cp,CMutableTransaction &mtx,CPubKey
 
 std::string FSMList()
 {
-    return(0);
+    return("");
 }
 
 std::string FSMCreate(uint64_t txfee,std::string name,std::string states)
@@ -169,7 +169,7 @@ std::string FSMCreate(uint64_t txfee,std::string name,std::string states)
         mtx.vout.push_back(CTxOut(nValue,CScript() << ParseHex(HexStr(mypk)) << OP_CHECKSIG));
         return(FinalizeCCTx(-1LL,cp,mtx,mypk,txfee,opret));
     } else fprintf(stderr,"cant find fsm inputs\n");
-    return(0);
+    return("");
 }
 
 std::string FSMInfo(uint256 fsmtxid)
@@ -178,7 +178,7 @@ std::string FSMInfo(uint256 fsmtxid)
     cp = CCinit(&C,EVAL_FSM);
     mypk = pubkey2pk(Mypubkey());
     fsmpk = GetUnspendable(cp,0);
-    return(0);
+    return("");
 }
 
 
diff --git a/src/cc/lotto.cpp b/src/cc/lotto.cpp
index 0d03d5e15..e20cb3505 100644
--- a/src/cc/lotto.cpp
+++ b/src/cc/lotto.cpp
@@ -164,7 +164,7 @@ std::string LottoTicket(uint64_t txfee,int64_t numtickets)
         mtx.vout.push_back(CTxOut(nValue,CScript() << ParseHex(HexStr(mypk)) << OP_CHECKSIG));
         return(FinalizeCCTx(-1LL,cp,mtx,mypk,txfee,opret));
     } else fprintf(stderr,"cant find Lotto inputs\n");
-    return(0);
+    return("");
 }
 
 std::string LottoWinner(uint64_t txfee)
@@ -180,7 +180,7 @@ std::string LottoWinner(uint64_t txfee)
         mtx.vout.push_back(MakeCC1vout(EVAL_LOTTO,winnings,Lottopk));
         return(FinalizeCCTx(0,cp,mtx,mypk,txfee,opret));
     }
-    return(0);
+    return("");
 }
 
 
diff --git a/src/cc/rewards.cpp b/src/cc/rewards.cpp
index c84c73591..896284245 100644
--- a/src/cc/rewards.cpp
+++ b/src/cc/rewards.cpp
@@ -424,12 +424,12 @@ std::string RewardsCreateFunding(uint64_t txfee,char *planstr,int64_t funds,int6
     if ( funds < COIN || mindeposit < 0 || minseconds < 0 || maxseconds < 0 )
     {
         fprintf(stderr,"negative parameter error\n");
-        return(0);
+        return("");
     }
     if ( APR > REWARDSCC_MAXAPR )
     {
         fprintf(stderr,"25%% APR is maximum\n");
-        return(0);
+        return("");
     }
     cp = CCinit(&C,EVAL_REWARDS);
     if ( txfee == 0 )
@@ -440,7 +440,7 @@ std::string RewardsCreateFunding(uint64_t txfee,char *planstr,int64_t funds,int6
     if ( RewardsPlanExists(cp,sbits,rewardspk,a,b,c,d) != 0 )
     {
         fprintf(stderr,"Rewards plan (%s) already exists\n",planstr);
-        return(0);
+        return("");
     }
     if ( AddNormalinputs(mtx,mypk,funds+2*txfee,64) > 0 )
     {
@@ -449,7 +449,7 @@ std::string RewardsCreateFunding(uint64_t txfee,char *planstr,int64_t funds,int6
         return(FinalizeCCTx(0,cp,mtx,mypk,txfee,EncodeRewardsFundingOpRet('F',sbits,APR,minseconds,maxseconds,mindeposit)));
     }
     fprintf(stderr,"cant find enough inputs\n");
-    return(0);
+    return("");
 }
 
 std::string RewardsAddfunding(uint64_t txfee,char *planstr,uint256 fundingtxid,int64_t amount)
@@ -458,7 +458,7 @@ std::string RewardsAddfunding(uint64_t txfee,char *planstr,uint256 fundingtxid,i
     if ( amount < 0 )
     {
         fprintf(stderr,"negative parameter error\n");
-        return(0);
+        return("");
     }
     cp = CCinit(&C,EVAL_REWARDS);
     if ( txfee == 0 )
@@ -469,7 +469,7 @@ std::string RewardsAddfunding(uint64_t txfee,char *planstr,uint256 fundingtxid,i
     if ( RewardsPlanExists(cp,sbits,rewardspk,a,b,c,d) == 0 )
     {
         fprintf(stderr,"Rewards plan %s doesnt exist\n",planstr);
-        return(0);
+        return("");
     }
     sbits = stringbits(planstr);
     if ( AddNormalinputs(mtx,mypk,amount+txfee,64) > 0 )
@@ -478,7 +478,7 @@ std::string RewardsAddfunding(uint64_t txfee,char *planstr,uint256 fundingtxid,i
         return(FinalizeCCTx(0,cp,mtx,mypk,txfee,EncodeRewardsOpRet('A',sbits,fundingtxid)));
     } else fprintf(stderr,"cant find enough inputs\n");
     fprintf(stderr,"cant find fundingtxid\n");
-    return(0);
+    return("");
 }
 
 std::string RewardsLock(uint64_t txfee,char *planstr,uint256 fundingtxid,int64_t deposit)
@@ -487,7 +487,7 @@ std::string RewardsLock(uint64_t txfee,char *planstr,uint256 fundingtxid,int64_t
     if ( deposit < 0 )
     {
         fprintf(stderr,"negative parameter error\n");
-        return(0);
+        return("");
     }
     cp = CCinit(&C,EVAL_REWARDS);
     if ( txfee == 0 )
@@ -498,12 +498,12 @@ std::string RewardsLock(uint64_t txfee,char *planstr,uint256 fundingtxid,int64_t
     if ( RewardsPlanExists(cp,sbits,rewardspk,APR,minseconds,maxseconds,mindeposit) == 0 )
     {
         fprintf(stderr,"Rewards plan %s doesnt exist\n",planstr);
-        return(0);
+        return("");
     }
     if ( deposit < mindeposit )
     {
         fprintf(stderr,"Rewards plan %s deposit %.8f < mindeposit %.8f\n",planstr,(double)deposit/COIN,(double)mindeposit/COIN);
-        return(0);
+        return("");
     }
     if ( (funding= RewardsPlanFunds(sbits,cp,rewardspk,fundingtxid)) >= deposit ) // arbitrary cmpval
     {
@@ -515,7 +515,7 @@ std::string RewardsLock(uint64_t txfee,char *planstr,uint256 fundingtxid,int64_t
         } else fprintf(stderr,"cant find enough inputs %.8f note enough for %.8f\n",(double)funding/COIN,(double)deposit/COIN);
     }
     fprintf(stderr,"cant find rewards inputs\n");
-    return(0);
+    return("");
 }
 
 std::string RewardsUnlock(uint64_t txfee,char *planstr,uint256 fundingtxid,uint256 locktxid)
@@ -530,7 +530,7 @@ std::string RewardsUnlock(uint64_t txfee,char *planstr,uint256 fundingtxid,uint2
     if ( RewardsPlanExists(cp,sbits,rewardspk,APR,minseconds,maxseconds,mindeposit) == 0 )
     {
         fprintf(stderr,"Rewards plan %s doesnt exist\n",planstr);
-        return(0);
+        return("");
     }
     fprintf(stderr,"APR %.8f minseconds.%llu maxseconds.%llu mindeposit %.8f\n",(double)APR/COIN,(long long)minseconds,(long long)maxseconds,(double)mindeposit/COIN);
     if ( locktxid == zeroid )
@@ -541,7 +541,7 @@ std::string RewardsUnlock(uint64_t txfee,char *planstr,uint256 fundingtxid,uint2
         if ( (amount= CCutxovalue(coinaddr,locktxid,0)) == 0 )
         {
             fprintf(stderr,"%s locktxid/v0 is spent\n",coinaddr);
-            return(0);
+            return("");
         }
         if ( GetTransaction(locktxid,tx,hashBlock,false) != 0 && tx.vout.size() > 0 && tx.vout[1].scriptPubKey.IsPayToCryptoCondition() == 0 )
         {
@@ -551,7 +551,7 @@ std::string RewardsUnlock(uint64_t txfee,char *planstr,uint256 fundingtxid,uint2
         else
         {
             fprintf(stderr,"%s no normal vout.1 in locktxid\n",coinaddr);
-            return(0);
+            return("");
         }
     }
     if ( amount > 0 && (reward= RewardsCalc(amount,mtx.vin[0].prevout.hash,APR,minseconds,maxseconds,mindeposit)) > txfee && scriptPubKey.size() > 0 )
@@ -568,6 +568,6 @@ std::string RewardsUnlock(uint64_t txfee,char *planstr,uint256 fundingtxid,uint2
         fprintf(stderr,"cant find enough rewards inputs\n");
     }
     fprintf(stderr,"amount %.8f -> reward %.8f\n",(double)amount/COIN,(double)reward/COIN);
-    return(0);
+    return("");
 }