# Unions Probably won't be used much, eh. Like a structure, but all members share the same (starting) memory address typedef union testUnion{ int Int; float Real; } A union is the size of it's biggest member (in bytes) A union will be one of these types, so either an int or float depending on what it's set as. This can be useful for APIs, or if a variable could be a number of types. More likely the former.