Help with converting small pseudo script to C# please?

My biggest question remains on how to 'select' specific cube prefabs from my grid using a brush technique. I had a functioning world generator using this script and the results were very good. Here is a small album. However, it used predefined functions and now that I am making the transfer over to Unity, I am at square one again with broken code.

Here is a screen shot of my WIP world generator

 Iterations = 80;
 Gain = 3;
 BrushSize = 128;
 //
 var n = Iterations;
 while n > 0 {
     var b = BrushSize;
     while b > 0 {
     
     // find random x,y coordinate within grid
         var Brush_X = random_range(0,Width)
         var Brush_Y = random_range(0,Height)
     
     // add random range between -Gain,+Gain to each cube prefab within area of BrushSize
     b--;
     }
 n--;
 }