1) Structure: The size in bytes is the sum total of size of 
all the elements in the structure, plus padding bytes.
2) Size of in bytes of the union is size of the largest 
variable element in the union. 

i.e In case of Union, the elements making up the 
union 'overlap' in memory OR they are accessed as diffrent 
name/type at diffrent places in the program.

Whereas in case of Struct, each of the elements have a 
distinct identity.