This function will close All open trades for a particual MagicNumber of EA.

Code:
void CloseAll()
{
int total = OrdersTotal();
for(int i=total-1;i>=0;i--)
{
OrderSelect(i, SELECT_BY_POS);
int type = OrderType();

if (OrderSymbol()==Symbol() && (OrderMagicNumber() == MagicNumber))
{
//-- Close open BUYs
if (type == OP_BUY) OrderClose(OrderTicket(),OrderLots(),MarketInfo(OrderSymbol(),MODE_BID),Slippage,CornflowerBlue);
//-- Close open SELLS
if (type == OP_SELL) OrderClose(OrderTicket(),OrderLots(),MarketInfo(OrderSymbol(),MODE_ASK),Slippage,CornflowerBlue);
}
}
return;
}