The function iBands doesn't give me the right values

Question

I have a problem with my code, I want to perform some actions when the price is above the upper Bollinger band, or below the lower one. But it excutes my actions after, and not a regular way, sometimes it will be 1 candle too late, or 4 candles after, etc. But not at the right time.

Here is what I do: if the last bar closed above the upper band, or below the lower band, I want to perform some actions. On the chart I can see very clearly that the price closed above or below the bands, but it does not excecute my actions on candle[0] (actual price) after candle[1] closed above or below the bands. Here is an example of my code (I don't write the actions in the conditions to make it shorter and more clear):

   double     BBlow = iBands(NULL,0,20,2,0,PRICE_CLOSE,MODE_LOWER,1);
   double     BBhigh = iBands(NULL,0,20,2,0,PRICE_CLOSE,MODE_UPPER,1);
   if (Close[1] > BBhigh)
       do this (sell for example);
   if (Close[1] < BBlow)
       do that (buy for example);