can anybody help me？regarding MT5 program..

[wang]

class CAccountInfo
{
public:
//--- fast access methods to the integer account propertyes
long Login();
ENUM_ACCOUNT_TRADE_MODE TradeMode();
string TradeModeString();
int Liverage();
ENUM_ACCOUNT_STOPOUT_MODE MarginMode();
string MarginModeString();
bool TradeAllowed();
bool TradeExpert();
//--- access methods to the API MQL5 functions
long InfoInteger(ENUM_ACCOUNT_INFO_INTEGER prop_id);
double InfoDouble(ENUM_ACCOUNT_INFO_DOUBLE prop_id);
string InfoString(ENUM_ACCOUNT_INFO_STRING prop_id);
double FreeMarginCheck(string Symbol,int trade_operation,double volume);
};

//+------------------------------------------------------------------+
//| Access functions AccountFreeMarginCheck(...). |
//| INPUT: name -symbol name, |
//| trade_operation -trade operation, |
//| volume -volume of the opening position. |
//| OUTPUT: the property value. |
//| REMARK: no. |

double CAccountInfo::FreeMarginCheck(string symbol,int trade_operation,double volume)
{
return(AccountFreeMarginCheck(symbol,trade_operation,volume));
}

can anybody do me a favourite? this is a part program of the MT5 sample. i got an error is "AccountFreeMarginCheck" is not defined during i trying to use it .i'm not very understand C++ program,therefore,i don't know how to defined it .the error of program is a very big headched for me,i can't contiune edit my new program if i can't solve this problem.pls,help !!!!!!