Compiler shows undefined structure error while declaring a class

class AddressBook
{
private:   
char firstname[20];
char lastname[20];
char no[15];

class adrs
{
public:
char postal[100];
char pincode[7];
friend void say();
friend void Add();
friend void Edit();
friend void View(int);
}address;
char dob[11];
char email[50];

public:
friend void say();
void sort(AddressBook []);
void NumberSort(AddressBook []);
void Add(void);
void Delete(AddressBook [], int pos);
void Edit();
void LinearSearch(AddressBook [], char a[]);
friend void ViewAll();
void View(int);
void FetchContact();
};

This is the declaration of a class for a contact-book program.

 void sort(AddressBook []);
 void NumberSort(AddressBook []); 
 void Delete(AddressBook [], int pos); 
 void LinearSearch(AddressBook [], char a[]);

These lines in the above declaration shows up as an error in TurboC++ compiler. Can anyone tell me why?