Structures can be implemented with functions and arrays. Moreover, structures can be implemented as the member of other structure. This is termed as structure within structure.  

When a structure is decleared as the member of another structue, it is called Structure within a structure. It is also known as nested structure.

One example of nested structure is given below:

struct date{
	// members of structure
        int day;
	int month;
	int year;
};

struct company{
	char name[20];
	long int employee_id;
	char sex[5];
	int age;
	struct date dob;};

#include<iostream.h>
#include<string.h>
#define MAX 1000

// structure block defination
struct date{
	// members of structure definition
	int day;
	int month;
	int year;
};

struct company{
	char name[20];
	long int employee_id;
	char sex[5];
	int age;
	// nested block defination
	struct date dob;

};

// structuer object defination
company employee[MAX];

// main function starts
int main(){

	company employee[MAX];

	int n;
	cout << "A program for collecting employee information";
	cout << endl;
	cout << "And displaying the collected information";
	cout << endl << endl;
	cout << "How many employees:";
	cin >> n;
	cout << endl;

	// functions defination
	void CollectInformtion(company employee[MAX], int n);
	void Display(company employee[MAX], int n);
	
	// functions calling
	CollectInformtion(employee, n);
	Display(employee, n);

	cin.get();
	return 0;
}

// collecting information form the user
void CollectInformtion(company employee[MAX], int n){

	cout << "Enter the following information:";
	cout << endl << endl;
	
	for (int i=1; i<=n; i++){
		cout << "Enter information for employee no: " << i;
		cout << endl;

		cout << "Name   :"; cin >> employee[i].name;
		cout << "ID     :"; cin >> employee[i].employee_id;
		cout << "Sex    :"; cin >> employee[i].sex;
		cout << "Age    :"; cin >> employee[i].age;
		cout << "Death of Birth:" << endl;
		cout << "Day    :";	cin >> employee[i].dob.day;
		cout << "Month  :"; cin >> employee[i].dob.month;
		cout << "Year   :";	cin >> employee[i].dob.year;
		
		cout << endl;
	}
}

// displaying entered information to the standard output
void Display(company employee[MAX], int n){

	cout << "Employee entered information:";
	cout << endl;
	cout << "Name	ID	Sex	Age	Date of Birth" << endl;

	for (int i=1; i<=n; i++){

		cout << employee[i].name		<< "\t";
		cout << employee[i].employee_id << "\t";
		cout << employee[i].sex; cout	<< "\t";
		cout << employee[i].age; cout	<< "\t";
		cout << employee[i].dob.day		<< ".";
		cout << employee[i].dob.month   << ".";
		cout << employee[i].dob.year    ;
		
		cout << endl;
	}
}

At first, the graphical representation of the program is given below:

So, the code block will be:

struct date{
	// members of structure
        int day;
	int month;
	int year;
};

struct company{
	char name[20];
	long int employee_id;
	char sex[5];
	int age;
	struct date dob;
};

Look "struct date dob;" is used to link the nested structure.

To initialize the values in nested structue it uses like the followings:

employee[i].dob.day;
employee[i].dob.month;
employee[i].dob.year;

The program has two functions:

void CollectInformtion(company employee[MAX], int n);
void Display(company employee[MAX], int n);

Function "CollectInformtion()" is used to take inputs from the users.And function "Display()" is used to display the final output.