WHAT IS DIFFERENCE BETWEEN ENUM,STRUCTURE AND UNION?

STRUCTURE:THESE CAN HAVE DIFFERENT DATA TYPES, STRUCTURE ALLOCATES MEMORY , TOTAL ADDITION OF ALL THE MEMBERS AND EACH MEMBER IS HAVING SEPARATE DATA BLOCKS

UNION:IN CASE OF UNION HAVING DIFFERENT DATA TYPE AND UNION ALLOCATION OF MEMORY IS DIFFERENT THAT SIZE WILL BE OF MAXMIMUM SIZE OF MEMBER IN UNION BLOCK ,AND ONE BLOCK IS ALLOCATED TO ALL DATA TYPES

ENUM:U CAN HAVE UR OWN DATA TYPES ,U CAN PROVIDE VALUE OF MEMBERS MANUALLY