how to check enums in C

let us say I have the following enum:

enum days{

MONDAY,

SUNDAY,

THURSDAY

} ;

I want to check if a struct that contains this enum has a valid value for example

typedef struct {

int date;

enum day name;

} complete_date;

so now I want to check if a complete_date has a valid enum

it can only be valid if it is MONDAY,SUNDAY, OR THURSDAY.

i want to assert that becuase if it has let us say TUESDAY i want to end the program;

i hope you can understand what I am trying to do.

this is a c programming question.

Thnaks