Need help with some coding in indicators

[bluxxmoon]

Hi I am trying to add 2SD 2 Standard deviation for the price ratio of two correlated pairs for example AUDUSD/NSDUSD , but getting zero result since it is not taking into array as the same way as it does in expert adviser. Please guide me where I am wrong.

These are the lines I am trying to get the standard deviation. Full working code mentioned below. I had found the code in one of the forums  and modified it to add the average line successfully. I am now stuck with trying to add 2SD + and minus so that the trade could be taken at 2SD and at 3SD take the SL. Any help will be deeply appreciated. 

   d[z] = iClose(sym1,0,z)/iClose(sym2,0,z);
   c = iStdDevOnArray(d,0,z,0,0,z);   

#property indicator_separate_window
#property indicator_buffers 3
#property indicator_color1 Yellow
#property indicator_color2 Red
#property indicator_color3 Blue



extern string sym1    = "AUDUSD";
extern string sym2    = "NZDUSD";
extern int barcount     = 5;

//---- buffers
double ExtMapBuffer1[];
double ExtMapBuffer2[];
double ExtMapBuffer3[];

//Global Variables
int ArrayIndex;
double ArraySum;
double a = 0;
double b=0;
double c=0;
double d[];



//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int init()
  {
//---- indicators
   SetIndexStyle(0,DRAW_LINE,EMPTY,2,clrYellow);
   SetIndexBuffer(0,ExtMapBuffer1);
   SetIndexStyle(1,DRAW_LINE,EMPTY,2,clrRed);
   SetIndexBuffer(1,ExtMapBuffer2);
   SetIndexStyle(2,DRAW_LINE,EMPTY,2,clrGreen);
   SetIndexBuffer(2,ExtMapBuffer3);
//----
   return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator deinitialization function                       |
//+------------------------------------------------------------------+
int deinit()
  {
//----
   
//----
   return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int start()

  {
   int counted_bars=IndicatorCounted();
//----
   for(int z=0;z<barcount;z++)
  {
  //Alert(z);
   a=iClose(sym1,0,z)+a;
   // Alert(d[0]);
   b=iClose(sym2,0,z)+b;
  
   d[z] = iClose(sym1,0,z)/iClose(sym2,0,z);
   c = iStdDevOnArray(d,0,z,0,0,z);   
  
   //Alert(d[0]);

   }
   
   for(int i=0;i<barcount;i++)
  {

   ExtMapBuffer1[i] = iClose(sym1,0,i)/iClose(sym2,0,i);
   ExtMapBuffer2[i] = (a/b);
  // ExtMapBuffer3[i] = (a/b)+(10*c);
   
   }
   
//----
   return(0);
  
  }

[Samuel Akinbowale]

https://www.mql5.com/en/code