diff --git a/OOP/03/Optional01.cpp b/OOP/03/Optional01.cpp
new file mode 100644
index 0000000..bcbd900
--- /dev/null
+++ b/OOP/03/Optional01.cpp
@@ -0,0 +1,66 @@
+#include <iostream>
+
+class Seller {
+private:
+    static int totalCount;
+    static double totalPrice;
+    int sellerNumber;
+    int sellCount;
+    double singlePrice;
+
+public:
+    Seller();
+    Seller(int sellerNum, int sellCount, double price);
+    int getSellerNumber();
+    int getSellCount();
+    double getSinglePrice();
+
+    static double calcAvg();
+    static double getTotal();
+};
+
+Seller::Seller() {
+    this->sellerNumber = 0;
+    this->sellCount = 0;
+    this->singlePrice = 0;
+}
+
+Seller::Seller(int sellerNum, int newSellCount, double price) {
+    this->sellerNumber = sellerNum;
+    this->sellCount = newSellCount;
+    this->singlePrice = price;
+    Seller::totalCount += newSellCount;
+    Seller::totalPrice += price * newSellCount;
+}
+
+int Seller::getSellerNumber() {
+    return this->sellerNumber;
+}
+
+int Seller::getSellCount() {
+    return this->sellCount;
+}
+
+double Seller::getSinglePrice() {
+    return this->singlePrice;
+}
+
+double Seller::getTotal() {
+    return Seller::totalPrice;
+}
+
+double Seller::calcAvg() {
+    return Seller::totalPrice / Seller::totalCount;
+}
+
+int Seller::totalCount = 0;
+double Seller::totalPrice = 0;
+
+int main() {
+    Seller* s1 = new Seller(101, 5, 23.5);
+    Seller* s2 = new Seller(102, 12, 24.5);
+    Seller* s3 = new Seller(103, 100, 21.5);
+    std::cout << "Total: " << Seller::getTotal() << std::endl;
+    std::cout << "Avg: " << Seller::calcAvg() << std::endl;
+    return 0;
+}
\ No newline at end of file
diff --git a/OOP/03/Optional03.cpp b/OOP/03/Optional03.cpp
new file mode 100644
index 0000000..521177d
--- /dev/null
+++ b/OOP/03/Optional03.cpp
@@ -0,0 +1,55 @@
+#include <iomanip>
+#include <iostream>
+
+class Date {
+private:
+    int d, m, y;
+
+public:
+    Date(int dd = 0, int mm = 0, int yy = 0);
+    Date(Date &D);
+    ~Date();
+    void display();
+};
+
+Date::Date(int dd, int mm, int yy) : d(dd), m(mm), y(yy) {
+    std::cout << "Constructor called! Address = 0x" << std::hex << std::setw(8)
+              << std::setfill('0') << this << std::endl;
+}
+
+Date::Date(Date &D) {
+    d = D.d;
+    m = D.m;
+    y = D.y;
+    std::cout << "Copy constructor called! Address = 0x" << std::hex
+              << std::setw(8) << std::setfill('0') << this << std::endl;
+}
+
+Date::~Date() {
+    std::cout << "Destructor called! Address = 0x" << std::hex << std::setw(8)
+              << std::setfill('0') << this << std::endl;
+}
+
+void Date::display() {
+    std::cout << "Displaying" << std::endl;
+}
+
+// Date func(Date A) {
+//     Date B(A);
+//     return B;
+// }
+
+// Date & func(Date A) {
+//     Date B(A);
+//     return B;
+// }
+
+Date func(Date A) {
+    return A;
+}
+
+int main() {
+    Date today;
+    today = func(today);
+    return 0;
+}
\ No newline at end of file
diff --git a/OOP/EmployeeAdmin/employee.h b/OOP/EmployeeAdmin/employee.h
index 5305538..61a5768 100644
--- a/OOP/EmployeeAdmin/employee.h
+++ b/OOP/EmployeeAdmin/employee.h
@@ -3,10 +3,11 @@ private:
     int individualEmpNo;
     int grade;
     int accumPay;
+    static int empCount;
 
 public:
     Employee();
-    Employee(int no, int newGrade, int newAccumPay);
+    Employee(int newGrade, int newAccumPay);
     ~Employee();
     void printInfo();
     void setEmpNo(int);
diff --git a/OOP/EmployeeAdmin/main.cpp b/OOP/EmployeeAdmin/main.cpp
index b10488d..b0fcff4 100644
--- a/OOP/EmployeeAdmin/main.cpp
+++ b/OOP/EmployeeAdmin/main.cpp
@@ -1,14 +1,18 @@
-#include <iostream>
 #include "employee.h"
+#include <iostream>
+
+int Employee::empCount = 0;
 
 Employee::Employee() {
-    this->individualEmpNo = 0;
+    Employee::empCount++;
+    this->individualEmpNo = empCount;
     this->grade = 0;
     this->accumPay = 0;
 }
 
-Employee::Employee(int no, int newGrade, int newAccumPay) {
-    this->individualEmpNo = no;
+Employee::Employee(int newGrade, int newAccumPay) {
+    Employee::empCount++;
+    this->individualEmpNo = Employee::empCount;
     this->grade = newGrade;
     this->accumPay = newAccumPay;
 }
@@ -18,7 +22,8 @@ Employee::~Employee() {
 }
 
 void Employee::printInfo() {
-    std::cout << "Employee No. " << this->individualEmpNo << ": grade " << this->grade << ", accumPay: " << this->accumPay << std::endl;
+    std::cout << "Employee No. " << this->individualEmpNo << ": grade "
+              << this->grade << ", accumPay: " << this->accumPay << std::endl;
 }
 
 void Employee::setEmpNo(int newNo) {
@@ -34,17 +39,17 @@ void Employee::setAccumPay(int newAccumPay) {
 }
 
 int main() {
-    Employee* staff[4];
-    staff[0] = new Employee();
-    staff[1] = new Employee(11343, 2, 2000);
-    staff[2] = new Employee(199, 1, 4000);
-    staff[3] = new Employee(59949, 4, 400);
+    Employee staff[20];
 
-    for (int i = 0; i < 4; i++) {
-        staff[i]->printInfo();
+    for (int i = 0; i < 20; i++) {
+        staff[i].setGrade(i + 1);
+        staff[i].setAccumPay((i + 1) * 10);
     }
+    
 
-    delete staff[3];
+    for (int i = 0; i < 20; i++) {
+        staff[i].printInfo();
+    }
 
     return 0;
 }
\ No newline at end of file