Please help I am trying to create an array for ratio but I receive an error

[Tatenda Maswedza]

2018.06.05 19:42:23.176 2016.03.01 00:03:30   array out of range in 'Ratio expert advisor.mq5' (54,20)

void OnTick()
  {
//---
   double Varience;
   double ChartArray[];
   double TheOtherCurrencyPairArray[];
   double RatioArray[];
   
   ArraySetAsSeries(TheOtherCurrencyPairArray,true);
   ArraySetAsSeries(ChartArray,true);
     
   CopyClose(Symbol(),time,0,lookbackperiod-1,ChartArray);
   CopyClose(TheOtherCurrencyPair,time,0,lookbackperiod-1,TheOtherCurrencyPairArray);
  
   
   
   for(int x= 0; x<lookbackperiod;x++)
      {
        double k  = ChartArray[x]/TheOtherCurrencyPairArray[x];
         RatioArray[x]= k;
      }
    
   Varience = MathVariance(RatioArray);
   

   
  
   
  }
//+------------------------------------------------------------------+

[Anthony Garot]

17003821:

2018.06.05 19:42:23.176 2016.03.01 00:03:30   array out of range in 'Ratio expert advisor.mq5' (54,20)

You need to set the size of the array.

Look at the ArrayResize() function.

[Tatenda Maswedza]

Anthony Garot:

You need to set the size of the array.

Look at the ArrayResize() function.

Thank you very much for your assistence, very sorry to trouble you where and how exactly do I resize the array.

[Anthony Garot]

17003821:
Thank you very much for your assistence, very sorry to trouble you where and how exactly do I resize the array.

   if ( ArrayResize(RatioArray,lookbackperiod-1) == -1 ) { Print("Failed to resize"); }

   for(int x=0; x<lookbackperiod - 1;x++)
     {
      double k=ChartArray[x]/TheOtherCurrencyPairArray[x];
      RatioArray[x]=k;
     }

[Marco vd Heijden]

Before you assign values to it.

[Tatenda Maswedza]

Marco vd Heijden:
Before you assign values to it.

Thank you very much