How to use Array in Expert?

I want to iMAOnArray(.........) in Expert. but not like in indicator, Arrary type Variable can not used in Expert, Why?
and how to .....

code in bellow:
 
double Buf_1[];  
double Buf_2[];  
int Start()
{
    for(i=0; i<=Bars; i++)
   {
       Buf_1[i] = iMA(....);     //if I Print Buf_1[i], it is 0 always !!!!!!!
   }
  for(i=0; i<=Bars; i++)
   {
       Buf_2[i] = iMAOnArray(Buf_1, ....);     //if I Print Buf_2[i], it is 0 always too !!!!!!!
   }
.....................
}

Thanks for your help!