diff --git a/20-OODesign/Ehtesham-Handouts.pdf b/20-OODesign/Ehtesham-Handouts.pdf
new file mode 100644
index 0000000..dd8e465
Binary files /dev/null and b/20-OODesign/Ehtesham-Handouts.pdf differ
diff --git a/20-OODesign/ehtesham1.cpp b/20-OODesign/ehtesham1.cpp
new file mode 100644
index 0000000..202c593
--- /dev/null
+++ b/20-OODesign/ehtesham1.cpp
@@ -0,0 +1,58 @@
+#include <iostream>
+#include <vector>
+#include <string>
+#include <cstdlib>
+using namespace std;
+
+// Since we have not learned exception handling...
+void error(string message) {
+	cerr << message << endl;
+	abort();
+}
+
+class Employee {
+public:
+	Employee(string id, string n) {
+		if (id == "" || n == "") error("Employee ID and name cannot be empty");
+		emp_id = id;
+		name = n;
+		bedehi = 0;
+	}
+private:
+	int bedehi;
+	string emp_id;
+	string name;
+};
+
+class MenuItem {
+public:
+	MenuItem(string t, int p) {
+		if (t == "") error("Menu item title cannot be empty");
+		if (p <= 0) error("Menu item price must be positive");
+		title = t;
+		price = p;
+	}
+private:
+	string title;
+	int price;
+};
+
+class Catering {
+public:
+	Catering(string n, vector<MenuItem> m) {
+		if (n == "") error("Catering name must be non-empty");
+		name = n;
+		menu = m;
+	}
+private:
+	string name;
+	vector<MenuItem> menu;
+};
+
+int main() {
+	Catering farsi("Farsi", { MenuItem("Kabab", 50000), MenuItem("Jooj", 30000) });
+	Catering alaa("Alaa", { MenuItem("Kabab", 40000), MenuItem("Maahi", 35000) });
+	Employee jamshid("1001", "Jamshid");
+	Employee mahvash("1002", "Mahvash");
+	Employee hooshang("1003", "Hooshang");
+}
\ No newline at end of file
diff --git a/20-OODesign/ehtesham2.cpp b/20-OODesign/ehtesham2.cpp
new file mode 100644
index 0000000..c5f4e66
--- /dev/null
+++ b/20-OODesign/ehtesham2.cpp
@@ -0,0 +1,74 @@
+#include <iostream>
+#include <vector>
+#include <string>
+#include <cstdlib>
+using namespace std;
+
+// Since we have not learned exception handling...
+void error(string message) {
+	cerr << message << endl;
+	abort();
+}
+
+class Employee {
+public:
+	Employee(string id, string n) {
+		if (id == "" || n == "") error("Employee ID and name cannot be empty");
+		emp_id = id;
+		name = n;
+		bedehi = 0;
+	}
+private:
+	int bedehi;
+	string emp_id;
+	string name;
+};
+
+class MenuItem {
+public:
+	MenuItem(string t, int p) {
+		if (t == "") error("Menu item title cannot be empty");
+		if (p <= 0) error("Menu item price must be positive");
+		title = t;
+		price = p;
+	}
+private:
+	string title;
+	int price;
+};
+
+class Catering {
+public:
+	Catering(string n, vector<MenuItem> m) {
+		name = n;
+		menu = m;
+	}
+private:
+	string name;
+	vector<MenuItem> menu;
+};
+
+class Ehtesham {
+public:
+	Ehtesham(vector<Catering> c, vector<Employee> e) {
+		caterings = c;
+		employees = e;
+	}
+private:
+	vector<Catering> caterings;
+	vector<Employee> employees;
+};
+
+int main() {
+	Ehtesham ehtesham(
+		{
+			Catering("Farsi", { MenuItem("Kabab", 50000), MenuItem("Jooj", 30000) }),
+			Catering("Alaa", { MenuItem("Kabab", 40000), MenuItem("Maahi", 35000) })
+		},
+		{
+			Employee("1001", "Jamshid"),
+			Employee("1002", "Mahvash"),
+			Employee("1003", "Hooshang")
+		}
+	);
+}
\ No newline at end of file
diff --git a/20-OODesign/ehtesham3.cpp b/20-OODesign/ehtesham3.cpp
new file mode 100644
index 0000000..934d09d
--- /dev/null
+++ b/20-OODesign/ehtesham3.cpp
@@ -0,0 +1,86 @@
+#include <iostream>
+#include <vector>
+#include <string>
+#include <cstdlib>
+using namespace std;
+
+// Since we have not learned exception handling...
+void error(string message) {
+	cerr << message << endl;
+	abort();
+}
+
+class Employee {
+public:
+	Employee(string id, string n) {
+		if (id == "" || n == "") error("Employee ID and name cannot be empty");
+		emp_id = id;
+		name = n;
+		bedehi = 0;
+	}
+private:
+	int bedehi;
+	string emp_id;
+	string name;
+};
+
+class MenuItem {
+public:
+	MenuItem(string t, int p) {
+		if (t == "") error("Menu item title cannot be empty");
+		if (p <= 0) error("Menu item price must be positive");
+		title = t;
+		price = p;
+	}
+private:
+	string title;
+	int price;
+};
+
+class EmployeeRequest {
+public:
+	EmployeeRequest(Employee* e, MenuItem* m) {
+		if (e == NULL || m == NULL) error("Employee request parameters must be non-null");
+		item = m;
+		emp = e;
+	}
+private:
+	Employee* emp;
+	MenuItem* item;
+};
+
+class Catering {
+public:
+	Catering(string n, vector<MenuItem> m) {
+		name = n;
+		menu = m;
+	}
+private:
+	string name;
+	vector<MenuItem> menu;
+};
+
+class Ehtesham {
+public:
+	Ehtesham(vector<Catering> c, vector<Employee> e) {
+		caterings = c;
+		employees = e;
+	}
+private:
+	vector<Catering> caterings;
+	vector<Employee> employees;
+};
+
+int main() {
+	Ehtesham ehtesham(
+		{
+			Catering("Farsi", { MenuItem("Kabab", 50000), MenuItem("Jooj", 30000) }),
+			Catering("Alaa", { MenuItem("Kabab", 40000), MenuItem("Maahi", 35000) })
+		},
+		{
+			Employee("1001", "Jamshid"),
+			Employee("1002", "Mahvash"),
+			Employee("1003", "Hooshang")
+		}
+	);
+}
\ No newline at end of file
diff --git a/20-OODesign/ehtesham4.cpp b/20-OODesign/ehtesham4.cpp
new file mode 100644
index 0000000..a6f5764
--- /dev/null
+++ b/20-OODesign/ehtesham4.cpp
@@ -0,0 +1,87 @@
+#include <iostream>
+#include <vector>
+#include <string>
+#include <cstdlib>
+using namespace std;
+
+// Since we have not learned exception handling...
+void error(string message) {
+	cerr << message << endl;
+	abort();
+}
+
+class Employee {
+public:
+	Employee(string id, string n) {
+		if (id == "" || n == "") error("Employee ID and name cannot be empty");
+		emp_id = id;
+		name = n;
+		bedehi = 0;
+	}
+private:
+	int bedehi;
+	string emp_id;
+	string name;
+};
+
+class MenuItem {
+public:
+	MenuItem(string t, int p) {
+		if (t == "") error("Menu item title cannot be empty");
+		if (p <= 0) error("Menu item price must be positive");
+		title = t;
+		price = p;
+	}
+private:
+	string title;
+	int price;
+};
+
+class EmployeeRequest {
+public:
+	EmployeeRequest(Employee* e, MenuItem* m) {
+		if (e == NULL || m == NULL) error("Employee request parameters must be non-null");
+		item = m;
+		emp = e;
+	}
+private:
+	Employee* emp;
+	MenuItem* item;
+};
+
+class Catering {
+public:
+	Catering(string n, vector<MenuItem> m) {
+		name = n;
+		menu = m;
+	}
+private:
+	string name;
+	vector<MenuItem> menu;
+	vector<EmployeeRequest> requests;
+};
+
+class Ehtesham {
+public:
+	Ehtesham(vector<Catering> c, vector<Employee> e) {
+		caterings = c;
+		employees = e;
+	}
+private:
+	vector<Catering> caterings;
+	vector<Employee> employees;
+};
+
+int main() {
+	Ehtesham ehtesham(
+		{
+			Catering("Farsi", { MenuItem("Kabab", 50000), MenuItem("Jooj", 30000) }),
+			Catering("Alaa", { MenuItem("Kabab", 40000), MenuItem("Maahi", 35000) })
+		},
+		{
+			Employee("1001", "Jamshid"),
+			Employee("1002", "Mahvash"),
+			Employee("1003", "Hooshang")
+		}
+	);
+}
diff --git a/20-OODesign/ehtesham5-dump.cpp b/20-OODesign/ehtesham5-dump.cpp
new file mode 100644
index 0000000..7e4aa60
--- /dev/null
+++ b/20-OODesign/ehtesham5-dump.cpp
@@ -0,0 +1,174 @@
+#include <iostream>
+#include <vector>
+#include <string>
+#include <cstdlib>
+#include <sstream>
+using namespace std;
+
+// Since we have not learned exception handling...
+void error(string message) {
+	cerr << message << endl;
+	abort();
+}
+
+class Employee {
+public:
+	Employee(string id, string n) {
+		if (id == "" || n == "") error("Employee ID and name cannot be empty");
+		emp_id = id;
+		name = n;
+		bedehi = 0;
+	}
+	string get_id() { return emp_id; }
+	string to_string() {
+		ostringstream os;
+		os << '[' << emp_id << "] " << name;
+		return os.str();
+	}
+private:
+	int bedehi;
+	string emp_id;
+	string name;
+};
+
+class MenuItem {
+public:
+	MenuItem(string t, int p) {
+		if (t == "") error("Menu item title cannot be empty");
+		if (p <= 0) error("Menu item price must be positive");
+		title = t;
+		price = p;
+	}
+	string get_title() { return title; }
+	string to_string() {
+		ostringstream os;
+		os << title << '(' << price << ')';
+		return os.str();
+	}
+private:
+	string title;
+	int price;
+};
+
+class EmployeeRequest {
+public:
+	EmployeeRequest(Employee* e, MenuItem* m) {
+		if (e == NULL || m == NULL) error("Employee request parameters must be non-null");
+		item = m;
+		emp = e;
+	}
+	string to_string() {
+		ostringstream os;
+		os << emp->to_string() << '\t' << item->to_string();
+		return os.str();
+	}
+private:
+	Employee* emp;
+	MenuItem* item;
+};
+
+class Catering {
+public:
+	Catering(string n, vector<MenuItem> m) {
+		name = n;
+		menu = m;
+	}
+	string get_name() { return name; }
+	
+	void add_employee_request(Employee* emp, string item_title) {
+		requests.push_back(EmployeeRequest(emp, find_item_by_title(item_title)));
+	}
+	string to_string() {
+		ostringstream os;
+		os << "Requests placed for catering " << name << endl;
+		for (EmployeeRequest request : requests)
+			os << request.to_string() << endl;
+		return os.str();
+	}	
+private:
+	MenuItem* find_item_by_title(string item_title) {
+		for (int i = 0; i < menu.size(); i++)
+			if (menu[i].get_title() == item_title)
+				return &menu[i];
+		error("cannot find menu item");
+	}
+
+	string name;
+	vector<MenuItem> menu;
+	vector<EmployeeRequest> requests;
+};
+
+class Ehtesham {
+public:
+	Ehtesham(vector<Catering> c, vector<Employee> e) {
+		caterings = c;
+		employees = e;
+	}
+	string to_string() {
+		ostringstream os;
+		os << "Employees:" << endl;
+		for (Employee employee : employees)
+			os << employee.to_string() << endl;
+		os << endl;
+		for (Catering catering : caterings)
+			os << catering.to_string() << endl;
+		return os.str();
+	}
+
+	void add_employee_request(string empid, string catering_name, string item) {
+		Catering* cat = find_catering_by_name(catering_name);
+		Employee* emp = find_employee_by_id(empid);
+		cat->add_employee_request(emp, item);
+	}
+private:
+	Employee* find_employee_by_id(string empid) {
+		for (int i = 0; i < employees.size(); i++)
+			if (employees[i].get_id() == empid)
+				return &employees[i];
+		error("cannot find employee");
+	}
+
+	Catering* find_catering_by_name(string name) {
+		for (int i = 0; i < caterings.size(); i++)
+			if (caterings[i].get_name() == name)
+				return &caterings[i];
+		error("cannot find catering");
+	}
+
+	vector<Catering> caterings;
+	vector<Employee> employees;
+};
+
+int main() {
+	Ehtesham ehtesham(
+		{
+			Catering("Farsi", { MenuItem("Kabab", 50000), MenuItem("Jooj", 30000) }),
+			Catering("Alaa", { MenuItem("Kabab", 40000), MenuItem("Maahi", 35000) })
+		},
+		{
+			Employee("1001", "Jamshid"),
+			Employee("1002", "Mahvash"),
+			Employee("1003", "Hooshang")
+		}
+	);
+
+	string command;
+	while (cin >> command) {
+		if (command == "request") {
+			string empid;
+			string catering;
+			string item;
+
+			cin >> empid >> catering >> item;
+			ehtesham.add_employee_request(empid, catering, item);
+		} else if (command == "dump") {
+			cout << ehtesham.to_string() << endl;
+		} else {
+			error("unknown command");
+		}
+	}
+}
+
+
+
+
diff --git a/20-OODesign/ehtesham5.cpp b/20-OODesign/ehtesham5.cpp
new file mode 100644
index 0000000..49e0010
--- /dev/null
+++ b/20-OODesign/ehtesham5.cpp
@@ -0,0 +1,139 @@
+#include <iostream>
+#include <vector>
+#include <string>
+#include <cstdlib>
+using namespace std;
+
+// Since we have not learned exception handling...
+void error(string message) {
+	cerr << message << endl;
+	abort();
+}
+
+class Employee {
+public:
+	Employee(string id, string n) {
+		if (id == "" || n == "") error("Employee ID and name cannot be empty");
+		emp_id = id;
+		name = n;
+		bedehi = 0;
+	}
+	string get_id() { return emp_id; }
+private:
+	int bedehi;
+	string emp_id;
+	string name;
+};
+
+class MenuItem {
+public:
+	MenuItem(string t, int p) {
+		if (t == "") error("Menu item title cannot be empty");
+		if (p <= 0) error("Menu item price must be positive");
+		title = t;
+		price = p;
+	}
+	string get_title() { return title; }
+private:
+	string title;
+	int price;
+};
+
+class EmployeeRequest {
+public:
+	EmployeeRequest(Employee* e, MenuItem* m) {
+		if (e == NULL || m == NULL) error("Employee request parameters must be non-null");
+		item = m;
+		emp = e;
+	}
+private:
+	Employee* emp;
+	MenuItem* item;
+};
+
+class Catering {
+public:
+	Catering(string n, vector<MenuItem> m) {
+		name = n;
+		menu = m;
+	}
+	string get_name() { return name; }
+	
+	void add_employee_request(Employee* emp, string item_title) {
+		requests.push_back(EmployeeRequest(emp, find_item_by_title(item_title)));
+	}
+private:
+	MenuItem* find_item_by_title(string item_title) {
+		for (int i = 0; i < menu.size(); i++)
+			if (menu[i].get_title() == item_title)
+				return &menu[i];
+		error("cannot find menu item");
+	}
+
+	string name;
+	vector<MenuItem> menu;
+	vector<EmployeeRequest> requests;
+};
+
+class Ehtesham {
+public:
+	Ehtesham(vector<Catering> c, vector<Employee> e) {
+		caterings = c;
+		employees = e;
+	}
+	
+	void add_employee_request(string empid, string catering_name, string item) {
+		Catering* cat = find_catering_by_name(catering_name);
+		Employee* emp = find_employee_by_id(empid);
+		cat->add_employee_request(emp, item);
+	}
+private:
+	Employee* find_employee_by_id(string empid) {
+		for (int i = 0; i < employees.size(); i++)
+			if (employees[i].get_id() == empid)
+				return &employees[i];
+		error("cannot find employee");
+	}
+
+	Catering* find_catering_by_name(string name) {
+		for (int i = 0; i < caterings.size(); i++)
+			if (caterings[i].get_name() == name)
+				return &caterings[i];
+		error("cannot find catering");
+	}
+
+	vector<Catering> caterings;
+	vector<Employee> employees;
+};
+
+int main() {
+	Ehtesham ehtesham(
+		{
+			Catering("Farsi", { MenuItem("Kabab", 50000), MenuItem("Jooj", 30000) }),
+			Catering("Alaa", { MenuItem("Kabab", 40000), MenuItem("Maahi", 35000) })
+		},
+		{
+			Employee("1001", "Jamshid"),
+			Employee("1002", "Mahvash"),
+			Employee("1003", "Hooshang")
+		}
+	);
+
+	string command;
+	while (cin >> command) {
+		if (command == "request") {
+			string empid;
+			string catering;
+			string item;
+
+			cin >> empid >> catering >> item;
+			ehtesham.add_employee_request(empid, catering, item);
+		} else {
+			error("unknown command");
+		}
+	}
+}
+
+
+
+
diff --git a/20-OODesign/ehtesham6.cpp b/20-OODesign/ehtesham6.cpp
new file mode 100644
index 0000000..a551bb9
--- /dev/null
+++ b/20-OODesign/ehtesham6.cpp
@@ -0,0 +1,281 @@
+#include <iostream>
+#include <vector>
+#include <set>
+#include <string>
+#include <cstdlib>
+#include <sstream>
+using namespace std;
+
+// Since we have not learned exception handling...
+void error(string message) {
+	cerr << message << endl;
+	abort();
+}
+
+class Employee {
+public:
+	Employee(string id, string n) {
+		if (id == "" || n == "") error("Employee ID and name cannot be empty");
+		emp_id = id;
+		name = n;
+		bedehi = 0;
+	}
+	string get_id() { return emp_id; }
+	int get_bedehi() { return bedehi; }
+
+	void charge(int amount) {
+		bedehi += amount;
+	}
+
+	string to_string() {
+		ostringstream os;
+		os << '[' << emp_id << "] " << name;
+		return os.str();
+	}
+private:
+	int bedehi;
+	string emp_id;
+	string name;
+};
+
+class MenuItem {
+public:
+	MenuItem(string t, int p) {
+		if (t == "") error("Menu item title cannot be empty");
+		if (p <= 0) error("Menu item price must be positive");
+		title = t;
+		price = p;
+	}
+	string get_title() { return title; }
+	int get_price() { return price; }
+	string to_string() {
+		ostringstream os;
+		os << title << '(' << price << ')';
+		return os.str();
+	}
+private:
+	string title;
+	int price;
+};
+
+class EmployeeRequest {
+public:
+	EmployeeRequest(Employee* e, MenuItem* m) {
+		if (e == NULL || m == NULL) error("Employee request parameters must be non-null");
+		item = m;
+		emp = e;
+	}
+	MenuItem* get_item() { return item; }
+	Employee* get_employee() { return emp; }
+	string to_string() {
+		ostringstream os;
+		os << emp->to_string() << '\t' << item->to_string();
+		return os.str();
+	}
+private:
+	Employee* emp;
+	MenuItem* item;
+};
+
+class CateringOrderLine {
+public:
+	CateringOrderLine(MenuItem* m, int q = 1) {
+		item = m;
+		quantity = q;
+	}
+	MenuItem* get_item() { return item; }
+
+	void increase_quantity(int q = 1) { quantity += q; }
+
+	string to_string() {
+		ostringstream os;
+		os << item->to_string() << " " << quantity;
+		return os.str();
+	}
+private:
+	MenuItem* item;
+	int quantity;
+};
+
+class CateringOrder {
+public:
+	void add_employee_request(EmployeeRequest req) {
+		for (CateringOrderLine& line : orderLines)
+			if (line.get_item() == req.get_item()) {
+				line.increase_quantity();
+				return;
+			}
+		orderLines.push_back(CateringOrderLine(req.get_item()));
+	}
+	string to_string() { 
+		ostringstream os;
+		for (CateringOrderLine line : orderLines)
+			os << '\t' << line.to_string() << endl;
+		return os.str();
+	}
+private:
+	vector<CateringOrderLine> orderLines;
+};
+
+class Catering {
+public:
+	Catering(string n, vector<MenuItem> m) {
+		name = n;
+		menu = m;
+	}
+	string get_name() { return name; }
+	string to_string() {
+		ostringstream os;
+		os << "Requests placed for catering " << name << endl;
+		for (EmployeeRequest request : requests)
+			os << request.to_string() << endl;
+		return os.str();
+	}
+	void add_employee_request(Employee* emp, string item_title) {
+		requests.push_back(EmployeeRequest(emp, find_item_by_title(item_title)));
+	}
+
+	CateringOrder gen_catering_order() {
+		CateringOrder order;
+		for (EmployeeRequest req : requests) {
+			order.add_employee_request(req);
+		}
+		return order;
+	}
+
+
+
+	void delivered(int delivery_cost) {
+		set<Employee*> employees;
+		for (EmployeeRequest request : requests) {
+			Employee* emp = request.get_employee();
+			emp->charge(request.get_item()->get_price());
+			employees.insert(emp);
+		}
+		for (Employee* emp : employees)
+			emp->charge(delivery_cost / employees.size());
+	}
+private:
+	MenuItem* find_item_by_title(string item_title) {
+		for (int i = 0; i < menu.size(); i++)
+			if (menu[i].get_title() == item_title)
+				return &menu[i];
+		error("cannot find menu item");
+	}
+
+	string name;
+	vector<MenuItem> menu;
+	vector<EmployeeRequest> requests;
+};
+
+class Ehtesham {
+public:
+	Ehtesham(vector<Catering> c, vector<Employee> e) {
+		caterings = c;
+		employees = e;
+	}
+	string to_string() {
+		ostringstream os;
+		os << "Employees:" << endl;
+		for (Employee employee : employees)
+			os << employee.to_string() << endl;
+		os << endl;
+		for (Catering catering : caterings)
+			os << catering.to_string() << endl;
+		return os.str();
+	}
+	void add_employee_request(string empid, string catering_name, string item) {
+		Catering* cat = find_catering_by_name(catering_name);
+		Employee* emp = find_employee_by_id(empid);
+		cat->add_employee_request(emp, item);
+	}
+
+
+
+	CateringOrder gen_catering_order(string catering_name) {
+		Catering* cat = find_catering_by_name(catering_name);
+		return cat->gen_catering_order();
+	}
+
+
+
+	void delivery_from(string catering_name, int delivery_cost) {
+		Catering* cat = find_catering_by_name(catering_name);
+		cat->delivered(delivery_cost);
+	}
+	string bedehi_report() {
+		ostringstream os;
+		for (Employee emp : employees) {
+			os << emp.to_string() << "\t" << emp.get_bedehi() << endl;
+		}
+		return os.str();
+	}
+private:
+	Employee* find_employee_by_id(string empid) {
+		for (int i = 0; i < employees.size(); i++)
+			if (employees[i].get_id() == empid)
+				return &employees[i];
+		error("cannot find employee");
+	}
+
+	Catering* find_catering_by_name(string name) {
+		for (int i = 0; i < caterings.size(); i++)
+			if (caterings[i].get_name() == name)
+				return &caterings[i];
+		error("cannot find catering");
+	}
+
+	vector<Catering> caterings;
+	vector<Employee> employees;
+};
+
+int main() {
+	Ehtesham ehtesham(
+		{
+			Catering("Farsi", { MenuItem("Kabab", 50000), MenuItem("Jooj", 30000) }),
+			Catering("Alaa", { MenuItem("Kabab", 40000), MenuItem("Maahi", 35000) })
+		},
+		{
+			Employee("1001", "Jamshid"),
+			Employee("1002", "Mahvash"),
+			Employee("1003", "Hooshang")
+		}
+	);
+
+	string command;
+	while (cin >> command) {
+		if (command == "request") {
+			string empid;
+			string catering;
+			string item;
+
+			cin >> empid >> catering >> item;
+			ehtesham.add_employee_request(empid, catering, item);
+
+			cout << "Request from employee " << empid << " handled!" << endl << endl;
+
+		} else if (command == "catorder") {
+			string catering_name;
+			cin >> catering_name;
+			CateringOrder order = ehtesham.gen_catering_order(catering_name);
+			cout << "Order for catering " << catering_name << ":\n";
+			cout << order.to_string() << endl;
+
+		} else if (command == "delivery") {
+			string catering_name;
+			int delivery_cost;
+
+			cin >> catering_name;
+			cin >> delivery_cost;
+			ehtesham.delivery_from(catering_name, delivery_cost);
+			cout << "Delivery from " << catering_name << " handled!" << endl << endl;
+		} else if (command == "bedehi") {
+			cout << "Bedehi Report: " << endl << ehtesham.bedehi_report() << endl;
+		} else if (command == "dump") {
+			cout << ehtesham.to_string() << endl;
+		} else {
+			cerr << "unknown command\n";
+			abort();
+		}
+	}
+}
\ No newline at end of file
diff --git a/20-OODesign/ehtesham7.cpp b/20-OODesign/ehtesham7.cpp
new file mode 100644
index 0000000..890ee28
--- /dev/null
+++ b/20-OODesign/ehtesham7.cpp
@@ -0,0 +1,289 @@
+#include <iostream>
+#include <vector>
+#include <set>
+#include <string>
+#include <cstdlib>
+#include <sstream>
+using namespace std;
+
+// Since we have not learned exception handling...
+void error(string message) {
+	cerr << message << endl;
+	abort();
+}
+
+class Employee {
+public:
+	Employee(string id, string n) {
+		if (id == "" || n == "") error("Employee ID and name cannot be empty");
+		emp_id = id;
+		name = n;
+		bedehi = 0;
+	}
+	string get_id() { return emp_id; }
+	int get_bedehi() { return bedehi; }
+
+	void charge(int amount) {
+		bedehi += amount;
+	}
+
+	string to_string() {
+		ostringstream os;
+		os << '[' << emp_id << "] " << name;
+		return os.str();
+	}
+private:
+	int bedehi;
+	string emp_id;
+	string name;
+};
+
+class MenuItem {
+public:
+	MenuItem(string t, int p) {
+		if (t == "") error("Menu item title cannot be empty");
+		if (p <= 0) error("Menu item price must be positive");
+		title = t;
+		price = p;
+	}
+	string get_title() { return title; }
+	int get_price() { return price; }
+	string to_string() {
+		ostringstream os;
+		os << title << '(' << price << ')';
+		return os.str();
+	}
+private:
+	string title;
+	int price;
+};
+
+class EmployeeRequest {
+public:
+	EmployeeRequest(Employee* e, MenuItem* m) {
+		if (e == NULL || m == NULL) error("Employee request parameters must be non-null");
+		item = m;
+		emp = e;
+	}
+	MenuItem* get_item() { return item; }
+	Employee* get_employee() { return emp; }
+	string to_string() {
+		ostringstream os;
+		os << emp->to_string() << '\t' << item->to_string();
+		return os.str();
+	}
+private:
+	Employee* emp;
+	MenuItem* item;
+};
+
+class CateringOrderLine {
+public:
+	CateringOrderLine(MenuItem* m, int q = 1) {
+		item = m;
+		quantity = q;
+	}
+	MenuItem* get_item() { return item; }
+
+	void increase_quantity(int q = 1) { quantity += q; }
+
+	string to_string() {
+		ostringstream os;
+		os << item->to_string() << " " << quantity;
+		return os.str();
+	}
+private:
+	MenuItem* item;
+	int quantity;
+};
+
+class CateringOrder {
+public:
+	void add_employee_request(EmployeeRequest req) {
+		for (CateringOrderLine& line : orderLines)
+			if (line.get_item() == req.get_item()) {
+				line.increase_quantity();
+				return;
+			}
+		orderLines.push_back(CateringOrderLine(req.get_item()));
+	}
+	string to_string() { 
+		ostringstream os;
+		for (CateringOrderLine line : orderLines)
+			os << '\t' << line.to_string() << endl;
+		return os.str();
+	}
+private:
+	vector<CateringOrderLine> orderLines;
+};
+
+class Catering {
+public:
+	Catering(string n, vector<MenuItem> m) {
+		name = n;
+		menu = m;
+	}
+	string get_name() { return name; }
+	string to_string() {
+		ostringstream os;
+		os << "Requests placed for catering " << name << endl;
+		for (EmployeeRequest request : requests)
+			os << request.to_string() << endl;
+		return os.str();
+	}
+	void add_employee_request(Employee* emp, string item_title) {
+		requests.push_back(EmployeeRequest(emp, find_item_by_title(item_title)));
+	}
+
+	CateringOrder gen_catering_order() {
+		CateringOrder order;
+		for (EmployeeRequest req : requests) {
+			order.add_employee_request(req);
+		}
+		return order;
+	}
+
+	void delivered(int delivery_cost) {
+		set<Employee*> employees;
+		for (EmployeeRequest request : requests) {
+			Employee* emp = request.get_employee();
+			emp->charge(request.get_item()->get_price());
+			employees.insert(emp);
+		}
+		for (Employee* emp : employees)
+			emp->charge(delivery_cost / employees.size());
+	}
+private:
+	MenuItem* find_item_by_title(string item_title) {
+		for (int i = 0; i < menu.size(); i++)
+			if (menu[i].get_title() == item_title)
+				return &menu[i];
+		error("cannot find menu item");
+		return NULL; // just to prevent warnings
+	}
+
+	string name;
+	vector<MenuItem> menu;
+	vector<EmployeeRequest> requests;
+};
+
+class Ehtesham {
+public:
+	Ehtesham(vector<Catering> c, vector<Employee> e) {
+		caterings = c;
+		employees = e;
+	}
+	string to_string() {
+		ostringstream os;
+		os << "Employees:" << endl;
+		for (Employee employee : employees)
+			os << employee.to_string() << endl;
+		os << endl;
+		for (Catering catering : caterings)
+			os << catering.to_string() << endl;
+		return os.str();
+	}
+
+	void add_employee_request(string empid, string catering_name, string item) {
+		Catering* cat = find_catering_by_name(catering_name);
+		Employee* emp = find_employee_by_id(empid);
+		cat->add_employee_request(emp, item);
+	}
+
+	CateringOrder gen_catering_order(string catering_name) {
+		Catering* cat = find_catering_by_name(catering_name);
+		return cat->gen_catering_order();
+	}
+
+	void delivery_from(string catering_name, int delivery_cost) {
+		Catering* cat = find_catering_by_name(catering_name);
+		cat->delivered(delivery_cost);
+	}
+
+	string bedehi_report() {
+		ostringstream os;
+		for (Employee emp : employees) {
+			os << emp.to_string() << "\t" << emp.get_bedehi() << endl;
+		}
+		return os.str();
+	}
+
+	void add_new_employee(string id, string name) {
+		employees.push_back(Employee(id, name));
+	}
+private:
+	Employee* find_employee_by_id(string empid) {
+		for (int i = 0; i < employees.size(); i++)
+			if (employees[i].get_id() == empid)
+				return &employees[i];
+		error("cannot find employee");
+		return NULL; // just to prevent warnings
+	}
+
+	Catering* find_catering_by_name(string name) {
+		for (int i = 0; i < caterings.size(); i++)
+			if (caterings[i].get_name() == name)
+				return &caterings[i];
+		error("cannot find catering");
+		return NULL; // just to prevent warnings
+	}
+
+	vector<Catering> caterings;
+	vector<Employee> employees;
+};
+
+int main() {
+	Ehtesham ehtesham(
+		{
+			Catering("Farsi", { MenuItem("Kabab", 50000), MenuItem("Jooj", 30000) }),
+			Catering("Alaa", { MenuItem("Kabab", 40000), MenuItem("Maahi", 35000) })
+		},
+		{
+			Employee("1001", "Jamshid"),
+			Employee("1002", "Mahvash"),
+			Employee("1003", "Hooshang")
+		}
+	);
+
+	string command;
+	while (cin >> command) {
+		if (command == "request") {
+			string empid;
+			string catering;
+			string item;
+
+			cin >> empid >> catering >> item;
+			ehtesham.add_employee_request(empid, catering, item);
+
+			cout << "Request from employee " << empid << " handled!" << endl << endl;
+
+		} else if (command == "catorder") {
+			string catering_name;
+			cin >> catering_name;
+			CateringOrder order = ehtesham.gen_catering_order(catering_name);
+			cout << "Order for catering " << catering_name << ":\n";
+			cout << order.to_string() << endl;
+
+		} else if (command == "delivery") {
+			string catering_name;
+			int delivery_cost;
+
+			cin >> catering_name;
+			cin >> delivery_cost;
+			ehtesham.delivery_from(catering_name, delivery_cost);
+			cout << "Delivery from " << catering_name << " handled!" << endl << endl;
+		} else if (command == "bedehi") {
+			cout << "Bedehi Report: " << endl << ehtesham.bedehi_report() << endl;
+		} else if (command == "newemployee") {
+			string empid;
+			string empname;
+			cin >> empid >> empname;
+			ehtesham.add_new_employee(empid, empname);
+		} else if (command == "dump") {
+			cout << ehtesham.to_string() << endl;
+		} else {
+			cerr << "unknown command\n";
+			abort();
+		}
+	}
+}
\ No newline at end of file
diff --git a/20-OODesign/ehtesham8.cpp b/20-OODesign/ehtesham8.cpp
new file mode 100644
index 0000000..1acaad4
--- /dev/null
+++ b/20-OODesign/ehtesham8.cpp
@@ -0,0 +1,297 @@
+#include <iostream>
+#include <vector>
+#include <set>
+#include <string>
+#include <cstdlib>
+#include <sstream>
+using namespace std;
+
+// Since we have not learned exception handling...
+void error(string message) {
+	cerr << message << endl;
+	abort();
+}
+
+class Employee {
+public:
+	Employee(string id, string n) {
+		if (id == "" || n == "") error("Employee ID and name cannot be empty");
+		emp_id = id;
+		name = n;
+		bedehi = 0;
+	}
+	string get_id() { return emp_id; }
+	int get_bedehi() { return bedehi; }
+
+	void charge(int amount) {
+		bedehi += amount;
+	}
+
+	string to_string() {
+		ostringstream os;
+		os << '[' << emp_id << "] " << name;
+		return os.str();
+	}
+private:
+	int bedehi;
+	string emp_id;
+	string name;
+};
+
+class MenuItem {
+public:
+	MenuItem(string t, int p) {
+		if (t == "") error("Menu item title cannot be empty");
+		if (p <= 0) error("Menu item price must be positive");
+		title = t;
+		price = p;
+	}
+	string get_title() { return title; }
+	int get_price() { return price; }
+	string to_string() {
+		ostringstream os;
+		os << title << '(' << price << ')';
+		return os.str();
+	}
+private:
+	string title;
+	int price;
+};
+
+class EmployeeRequest {
+public:
+	EmployeeRequest(Employee* e, MenuItem* m) {
+		if (e == NULL || m == NULL) error("Employee request parameters must be non-null");
+		item = m;
+		emp = e;
+	}
+	MenuItem* get_item() { return item; }
+	Employee* get_employee() { return emp; }
+	string to_string() {
+		ostringstream os;
+		os << emp->to_string() << '\t' << item->to_string();
+		return os.str();
+	}
+private:
+	Employee* emp;
+	MenuItem* item;
+};
+
+class CateringOrderLine {
+public:
+	CateringOrderLine(MenuItem* m, int q = 1) {
+		item = m;
+		quantity = q;
+	}
+	MenuItem* get_item() { return item; }
+
+	void increase_quantity(int q = 1) { quantity += q; }
+
+	string to_string() {
+		ostringstream os;
+		os << item->to_string() << " " << quantity;
+		return os.str();
+	}
+private:
+	MenuItem* item;
+	int quantity;
+};
+
+class CateringOrder {
+public:
+	void add_employee_request(EmployeeRequest req) {
+		for (CateringOrderLine& line : orderLines)
+			if (line.get_item() == req.get_item()) {
+				line.increase_quantity();
+				return;
+			}
+		orderLines.push_back(CateringOrderLine(req.get_item()));
+	}
+	string to_string() { 
+		ostringstream os;
+		for (CateringOrderLine line : orderLines)
+			os << '\t' << line.to_string() << endl;
+		return os.str();
+	}
+private:
+	vector<CateringOrderLine> orderLines;
+};
+
+class Catering {
+public:
+	Catering(string n, vector<MenuItem> m) {
+		name = n;
+		menu = m;
+	}
+	string get_name() { return name; }
+	string to_string() {
+		ostringstream os;
+		os << "Requests placed for catering " << name << endl;
+		for (EmployeeRequest request : requests)
+			os << request.to_string() << endl;
+		return os.str();
+	}
+	void add_employee_request(Employee* emp, string item_title) {
+		requests.push_back(EmployeeRequest(emp, find_item_by_title(item_title)));
+	}
+
+	CateringOrder gen_catering_order() {
+		CateringOrder order;
+		for (EmployeeRequest req : requests) {
+			order.add_employee_request(req);
+		}
+		return order;
+	}
+
+	void delivered(int delivery_cost) {
+		set<Employee*> employees;
+		for (EmployeeRequest request : requests) {
+			Employee* emp = request.get_employee();
+			emp->charge(request.get_item()->get_price());
+			employees.insert(emp);
+		}
+		for (Employee* emp : employees)
+			emp->charge(delivery_cost / employees.size());
+	}
+private:
+	MenuItem* find_item_by_title(string item_title) {
+		for (int i = 0; i < menu.size(); i++)
+			if (menu[i].get_title() == item_title)
+				return &menu[i];
+		error("cannot find menu item");
+		return NULL; // just to prevent warnings
+	}
+
+	string name;
+	vector<MenuItem> menu;
+	vector<EmployeeRequest> requests;
+};
+
+class Ehtesham {
+public:
+	Ehtesham(vector<Catering*> c, vector<Employee*> e) {
+		caterings = c;
+		employees = e;
+	}
+	string to_string() {
+		ostringstream os;
+		os << "Employees:" << endl;
+		for (Employee* employee : employees)
+			os << employee->to_string() << endl;
+		os << endl;
+		for (Catering* catering : caterings)
+			os << catering->to_string() << endl;
+		return os.str();
+	}
+
+	void add_employee_request(string empid, string catering_name, string item) {
+		Catering* cat = find_catering_by_name(catering_name);
+		Employee* emp = find_employee_by_id(empid);
+		cat->add_employee_request(emp, item);
+	}
+
+	CateringOrder gen_catering_order(string catering_name) {
+		Catering* cat = find_catering_by_name(catering_name);
+		return cat->gen_catering_order();
+	}
+
+	void delivery_from(string catering_name, int delivery_cost) {
+		Catering* cat = find_catering_by_name(catering_name);
+		cat->delivered(delivery_cost);
+	}
+
+	string bedehi_report() {
+		ostringstream os;
+		for (Employee* emp : employees) {
+			os << emp->to_string() << "\t" << emp->get_bedehi() << endl;
+		}
+		return os.str();
+	}
+
+	void add_new_employee(string id, string name) {
+		employees.push_back(new Employee(id, name));
+	}
+
+	void delete_everything() {
+		for (Catering* catering : caterings)
+			delete catering;
+		for (Employee* employee : employees)
+			delete employee;
+	}
+private:
+	Employee* find_employee_by_id(string empid) {
+		for (int i = 0; i < employees.size(); i++)
+			if (employees[i]->get_id() == empid)
+				return employees[i];
+		error("cannot find employee");
+		return NULL; // just to prevent warnings
+	}
+
+	Catering* find_catering_by_name(string name) {
+		for (Catering* catering : caterings)
+			if (catering->get_name() == name)
+				return catering;
+		error("cannot find catering");
+		return NULL; // just to prevent warnings
+	}
+
+	vector<Catering*> caterings;
+	vector<Employee*> employees;
+};
+
+int main() {
+	Ehtesham ehtesham(
+		{
+			new Catering("Farsi", { MenuItem("Kabab", 50000), MenuItem("Jooj", 30000) }),
+			new Catering("Alaa", { MenuItem("Kabab", 40000), MenuItem("Maahi", 35000) })
+		},
+		{
+			new Employee("1001", "Jamshid"),
+			new Employee("1002", "Mahvash"),
+			new Employee("1003", "Hooshang")
+		}
+	);
+
+	string command;
+	while (cin >> command) {
+		if (command == "request") {
+			string empid;
+			string catering;
+			string item;
+
+			cin >> empid >> catering >> item;
+			ehtesham.add_employee_request(empid, catering, item);
+
+			cout << "Request from employee " << empid << " handled!" << endl << endl;
+
+		} else if (command == "catorder") {
+			string catering_name;
+			cin >> catering_name;
+			CateringOrder order = ehtesham.gen_catering_order(catering_name);
+			cout << "Order for catering " << catering_name << ":\n";
+			cout << order.to_string() << endl;
+
+		} else if (command == "delivery") {
+			string catering_name;
+			int delivery_cost;
+
+			cin >> catering_name;
+			cin >> delivery_cost;
+			ehtesham.delivery_from(catering_name, delivery_cost);
+			cout << "Delivery from " << catering_name << " handled!" << endl << endl;
+		} else if (command == "bedehi") {
+			cout << "Bedehi Report: " << endl << ehtesham.bedehi_report() << endl;
+		} else if (command == "newemployee") {
+			string empid;
+			string empname;
+			cin >> empid >> empname;
+			ehtesham.add_new_employee(empid, empname);
+		} else if (command == "dump") {
+			cout << ehtesham.to_string() << endl;
+		} else {
+			cerr << "unknown command\n";
+			abort();
+		}
+	}
+	ehtesham.delete_everything();
+}
\ No newline at end of file
diff --git a/20-OODesign/input1.txt b/20-OODesign/input1.txt
new file mode 100644
index 0000000..adee33d
--- /dev/null
+++ b/20-OODesign/input1.txt
@@ -0,0 +1,4 @@
+request		1001	Farsi	Kabab
+request		1002	Farsi	Kabab
+request		1003	Alaa	Maahi
+request		1002	Farsi	Jooj
diff --git a/20-OODesign/input2.txt b/20-OODesign/input2.txt
new file mode 100644
index 0000000..691341c
--- /dev/null
+++ b/20-OODesign/input2.txt
@@ -0,0 +1,5 @@
+request		1001	Farsi	Kabab
+request		1002	Farsi	Kabab
+request		1003	Alaa	Maahi
+request		1002	Farsi	Jooj
+dump
diff --git a/20-OODesign/input3.txt b/20-OODesign/input3.txt
new file mode 100644
index 0000000..db25c37
--- /dev/null
+++ b/20-OODesign/input3.txt
@@ -0,0 +1,10 @@
+request		1001	Farsi	Kabab
+request		1002	Farsi	Kabab
+request		1003	Alaa	Maahi
+request		1002	Farsi	Jooj
+catorder	Farsi
+catorder	Alaa
+delivery	Farsi	10000
+bedehi
+delivery	Alaa	10000
+bedehi
\ No newline at end of file
diff --git a/20-OODesign/input4.txt b/20-OODesign/input4.txt
new file mode 100644
index 0000000..fc5effa
--- /dev/null
+++ b/20-OODesign/input4.txt
@@ -0,0 +1,11 @@
+request		1001	Farsi	Kabab
+request		1002	Farsi	Kabab
+request		1003	Alaa	Maahi
+request		1002	Farsi	Jooj
+catorder	Farsi
+catorder	Alaa
+newemployee 1004	Hakeem
+delivery	Farsi	10000
+bedehi
+delivery	Alaa	10000
+bedehi