Can we put void OnInit() and int OnCalculate() in one page?

When I write this code in MetaEditor:

#include <Trade\Trade.mqh>
CTrade md;
void OnInit()
{         
   md.BuyLimit(0.01, 3370, _Symbol, 0, 0,ORDER_TIME_DAY, 0, NULL);
}

It works. But when I add some codes to display "RSI", it doesn't work:

#include <Trade\Trade.mqh>
CTrade md;
void OnInit()
{         
   md.BuyLimit(0.01, 3370, _Symbol, 0, 0,ORDER_TIME_DAY, 0, NULL);
}

int i_COUNT, i_HANDLE, i_MA_PERIOD, i_START_POS;  
double db_ARRAY_RSI[];                            
int OnCalculate(const int rates_total,
                const int prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int &spread[])
{
   i_MA_PERIOD = 14;                              
   i_HANDLE = iRSI(Symbol(), PERIOD_CURRENT, i_MA_PERIOD, PRICE_CLOSE); 
   i_START_POS = 0;                              
   i_COUNT = 1;                                 
   CopyBuffer(i_HANDLE, 0, i_START_POS, i_COUNT, db_ARRAY_RSI);      
   Comment("db_ARRAY_RSI[0]: ", NormalizeDouble(db_ARRAY_RSI[0], 2), "abc"); 
   return(rates_total); 
}

My question is this: Can't we put both "void OnInit()" and "int OnCalculate()" in one expert?

I want to display "RSI" on the chart. How can I do that?

Solution

Expert Advisors (programs that trade) cannot have OnCalculate functions.
OnInit function must be an int and you return INIT_FAILED if the indicator cannot be loaded.

So this is the solution :

#include <Trade\Trade.mqh>
CTrade trade;
input int rsiPeriod=14;//period
int rsiHandle=INVALID_HANDLE;
int rsiWindow=-1;
int OnInit()
  {
  Print(EnumToString((ENUM_SYMBOL_INFO_INTEGER)18));
  //start rsi indicator 
    rsiHandle=iRSI(_Symbol,_Period,rsiPeriod,PRICE_CLOSE);
    if(rsiHandle!=INVALID_HANDLE){
    //add the indicator 
      int windows=(int)ChartGetInteger(0,CHART_WINDOWS_TOTAL);
      if(ChartIndicatorAdd(0,windows,rsiHandle)){
        rsiWindow=windows;
        }else{Alert("Cannot add rsi");ExpertRemove();return(INIT_FAILED);}
    }else{Alert("Cannot start rsi");ExpertRemove();return(INIT_FAILED);
    }
  return(INIT_SUCCEEDED);
  }
void OnTick()
  {
  //get rsi value 
    double value_return[];
    if(CopyBuffer(rsiHandle,0,0,1,value_return)==1){
      Comment("RSI "+DoubleToString(value_return[0],2));
      }
  }
void OnDeinit(const int reason)
  {
  if(rsiWindow>=1&&rsiHandle!=INVALID_HANDLE){
    ChartIndicatorDelete(0,rsiWindow,"RSI("+IntegerToString(rsiPeriod)+")");
    IndicatorRelease(rsiHandle);
    }
  }