update query don't work

I have a problem withe the query :
Code:

MyActionQuery->prepare("UPDATE Ahmed.creditor SET crebalance = '"+AmeelNewbal+"' where CRECODE = '"+ZoalCode+"'");[CODE]
[/CODE]

it gave me the error :

D:\KhalidQtAppllns\Applications\IsamSales\LOVdialo g.cpp:121: error: invalid operands of types 'const char [41]' and 'double' to binary 'operator+'
Code:

MyActionQuery->prepare("UPDATE Ahmed.creditor SET crebalance = '"+AmeelNewbal+"' where CRECODE = '"+ZoalCode+"'");
^
crebalance is a table field of type number, AmeelNewbal is a double variable, ZoalCode is a variable of type char and crecode is a primary key of type char

I'm connecting with Oracle 11g

Can any one help me about it ...!!!!

Thank You in advance ...