When a dynamic array with a class for a base type is declared, which constructor is called?

The default constructor is called for each element of the array. So if you declare an array with 100 elements (object instantiations), the constructor is executed 100 times!

Sorry do not know but if you need with math, i will

Well, this code would box the whole body of an html document. by using the relative value for position, you are telling it to position relative to its normal position, which the top left corner is at (0,0). by using left: 50px, you are telling the box to set the left margin  edge to 50px and by using top: 50px, you are telling it to set the top margin edge to 50px. by doing this shifting, the top left corner of the box, which is at (0,0) would be positioned at (50,50)