structure is abstract data type!
structures are used to represent data in user defined type.
each member of structure is allocated separate memory, for memory optimization memory padding is to be considered.
contrary in a union memory is not allocated to each member variable, instead to member which occupies highest amount of memory, the same memory is used among all the members.
1. Structure is user defined data type, by means we can store different type of data.
2. The most important difference between structure and union is in the size. Size of structure is the size of all the elements withing the structure where as the size of union is the size of highest element within it.