Can you declare struct and union one inside another?

The answer is false. A union can be nested in a structure . Actually union and structure can be nested in each other which means that nesting union in structure and nesting structure in union, both are possible.

You can declare a structure or union type separately from the definition of variables of that type , as described in Structure and union type definition and Structure and union variable declarations; or you can define a structure or union data type and all variables that have that type in one statement, as described in …

You use a union when your “thing” can be one of many different things but only one at a time. You use a structure when your “thing” should be a group of other things.

The answer is false. A union can be nested in a structure . Actually union and structure can be nested in each other which means that nesting union in structure and nesting structure in union, both are possible.