A little help with a coding error

Hi guys, could please someone fix this error.

I am trying to use this code, but it contains an error. It said "Illegal switch expression type"

Could someone please help me fixing this.

Thanks in advance

double iM =MarketInfo(Symbol(),MODE_PROFITCALCMODE);

switch(iM)

{

   case 0:sMarket = "FOREX";break;

   case 1:sMarket = "CFD";break;

   case 2:sMarket = "Futures";break;

   default:sMarket = iM;

}