diff --git a/part_4/4.1/1.go b/part_4/4.1/1.go
new file mode 100644
index 0000000..1c49a7a
--- /dev/null
+++ b/part_4/4.1/1.go
@@ -0,0 +1,11 @@
+import "fmt"
+
+func main() {
+	names := []string{
+		"Alex",
+		"Max",
+		"German",
+	}
+
+	fmt.Printf("My name is %v", names[3])
+}
diff --git a/part_4/4.1/2.go b/part_4/4.1/2.go
new file mode 100644
index 0000000..71a6ee2
--- /dev/null
+++ b/part_4/4.1/2.go
@@ -0,0 +1,32 @@
+package main
+
+import "fmt"
+
+type Person struct {
+	name string
+	age  uint8
+}
+
+func (p *Person) getName() string {
+	return p.name
+}
+
+func (p *Person) getAge() uint8 {
+	return p.age
+}
+
+func (p *Person) incAge() {
+	p.age++
+}
+
+func main() {
+	alex := &Person{
+		name: "Alex",
+		age:  26,
+	}
+	fmt.Printf("Person data: %+v\n", alex)
+	alex.incAge()
+	fmt.Printf("Person data: %+v\n", alex)
+	alex = nil
+	alex.incAge()
+}
diff --git a/part_4/4.2/1.go b/part_4/4.2/1.go
new file mode 100644
index 0000000..7600bb3
--- /dev/null
+++ b/part_4/4.2/1.go
@@ -0,0 +1,27 @@
+package main
+
+import "fmt"
+
+type Person struct {
+	name string
+	age  uint8
+}
+
+func (p *Person) incAge() {
+	p.age++
+	if p.age > 30 {
+		panic(fmt.Sprintf("%s too old!!!", p.name))
+	}
+}
+
+func main() {
+
+	alex := &Person{
+		name: "Alex",
+		age:  27,
+	}
+	for i := 0; i < 6; i++ {
+		alex.incAge()
+	}
+	fmt.Printf("Person data: %+v\n", alex)
+}
diff --git a/part_4/4.3/1.go b/part_4/4.3/1.go
new file mode 100644
index 0000000..a70cd11
--- /dev/null
+++ b/part_4/4.3/1.go
@@ -0,0 +1,33 @@
+package main
+
+import "fmt"
+
+type Person struct {
+	name string
+	age  uint8
+}
+
+func (p *Person) incAge() {
+	p.age++
+	if p.age > 30 {
+		defer func() {
+			fmt.Println("Calling defer function")
+		}()
+		panic(fmt.Sprintf("%s too old!!!", p.name))
+		defer func() { // нет смысла в вызове отложенной функции после паники
+			fmt.Println("Useless function")
+		}()
+	}
+}
+
+func main() {
+
+	alex := &Person{
+		name: "Alex",
+		age:  27,
+	}
+	for i := 0; i < 6; i++ {
+		alex.incAge()
+	}
+	fmt.Printf("Person data: %+v\n", alex)
+}
diff --git a/part_4/4.4/1.go b/part_4/4.4/1.go
new file mode 100644
index 0000000..b6b662c
--- /dev/null
+++ b/part_4/4.4/1.go
@@ -0,0 +1,35 @@
+package main
+
+import (
+	"fmt"
+	"log"
+)
+
+type Person struct {
+	name string
+	age  uint8
+}
+
+func (p *Person) incAge() {
+	p.age++
+	if p.age > 30 {
+		defer func() {
+			if err := recover(); err != nil {
+				log.Printf("%s has a new life, he (she) is %d years old", p.name, p.age)
+			}
+		}()
+		panic(fmt.Sprintf("%s too old!!!", p.name))
+	}
+}
+
+func main() {
+
+	alex := &Person{
+		name: "Alex",
+		age:  27,
+	}
+	for i := 0; i < 6; i++ {
+		alex.incAge()
+	}
+	fmt.Printf("Person data: %+v\n", alex)
+}
diff --git a/part_4/4.4/2.go b/part_4/4.4/2.go
new file mode 100644
index 0000000..f273702
--- /dev/null
+++ b/part_4/4.4/2.go
@@ -0,0 +1,44 @@
+package main
+
+import (
+	"fmt"
+	"log"
+)
+
+type Person struct {
+	name string
+	age  uint8
+}
+
+func (p *Person) incAge() {
+	p.age++
+	if p.age > 30 {
+		defer func() {
+			if err := recover(); err != nil {
+				log.Printf("%s has a new life, he (she) is %d years old", p.name, p.age)
+				if p.age > 35 {
+					panic(fmt.Sprintf("%s super old!!!", p.name))
+				}
+			}
+		}()
+		panic(fmt.Sprintf("%s too old!!!", p.name))
+	}
+}
+
+func main() {
+
+	alex := &Person{
+		name: "Alex",
+		age:  27,
+	}
+
+	defer func() {
+		if err := recover(); err != nil {
+			log.Printf("%s, welcome to club: 'А вот в наши времена'", alex.name)
+		}
+	}()
+	for i := 0; i < 20; i++ {
+		alex.incAge()
+	}
+	fmt.Printf("Person data: %+v\n", alex)
+}
diff --git a/part_4/4.5/1.go b/part_4/4.5/1.go
new file mode 100644
index 0000000..f8ba208
--- /dev/null
+++ b/part_4/4.5/1.go
@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func main() {
+	var str string = "10"
+	value, err := strconv.Atoi(str) // преобразование строки в целочисленное значение
+	if err != nil {                 // если err != nil, то обрабатываем ошибку
+		value = 22
+	}
+	fmt.Println(value) // 10
+
+	str = "2we"
+	value, err = strconv.Atoi(str)
+	if err != nil { // если err != nil, то обрабатываем ошибку
+		value = 22
+	}
+	fmt.Println(value) // 22
+}
diff --git a/part_4/4.5/2.go b/part_4/4.5/2.go
new file mode 100644
index 0000000..734ba53
--- /dev/null
+++ b/part_4/4.5/2.go
@@ -0,0 +1,12 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+func main() {
+	myError1 := errors.New("first error")
+	myError2 := fmt.Errorf("second error")
+	fmt.Println(myError1, myError2) // first error second error
+}
diff --git a/part_4/4.5/3.go b/part_4/4.5/3.go
new file mode 100644
index 0000000..62eda47
--- /dev/null
+++ b/part_4/4.5/3.go
@@ -0,0 +1,25 @@
+package main
+
+import "fmt"
+
+func div(a, b int) (int, error) {
+	if b == 0 {
+		return 0, fmt.Errorf("Сan't divide '%v' by zero", a)
+	}
+	return a / b, nil
+}
+
+func printResult(result int, err error) {
+	if err != nil {
+		fmt.Println(err)
+	} else {
+		fmt.Println(result)
+	}
+}
+
+func main() {
+	a, b := 10, 2
+	printResult(div(a, b)) // 5
+	a, b = 4, 0
+	printResult(div(a, b)) // Сan't divide '4' by zero
+}
diff --git a/part_4/4.6/1.go b/part_4/4.6/1.go
new file mode 100644
index 0000000..90c8f91
--- /dev/null
+++ b/part_4/4.6/1.go
@@ -0,0 +1,31 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+// Объявление пользовательского варианта ошибки деления на ноль
+var ErrDivByZero = errors.New("divide by zero")
+
+func div(a, b int) (int, error) {
+	if b == 0 {
+		return 0, ErrDivByZero
+	}
+	return a / b, nil
+}
+
+func printResult(result int, err error) {
+	if err != nil {
+		fmt.Println(err)
+	} else {
+		fmt.Println(result)
+	}
+}
+
+func main() {
+	a, b := 10, 2
+	printResult(div(a, b)) // 5
+	a, b = 4, 0
+	printResult(div(a, b)) // divide by zero
+}
diff --git a/part_4/4.7/1.go b/part_4/4.7/1.go
new file mode 100644
index 0000000..95e616c
--- /dev/null
+++ b/part_4/4.7/1.go
@@ -0,0 +1,41 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+var ErrDivByZero = errors.New("divide by zero")
+var ErrDivByOne = errors.New("divide by one")
+
+func div(a, b int) (int, error) {
+	if b == 0 {
+		return 0, ErrDivByZero
+	}
+	if b == 1 {
+		return a, ErrDivByOne
+	}
+	return a / b, nil
+}
+
+func printResult(result int, err error) {
+	if err != nil {
+		switch {
+		case errors.Is(err, ErrDivByZero):
+			fmt.Println(err)
+		case errors.Is(err, ErrDivByOne):
+			fmt.Printf("result = %d, but was %v\n", result, err)
+		default:
+			fmt.Printf("unexpected error: %v\n", err)
+		}
+
+	} else {
+		fmt.Println(result)
+	}
+}
+
+func main() {
+	printResult(div(10, 2)) // 5
+	printResult(div(4, 0))  // divide by zero
+	printResult(div(12, 1)) // result = 12, but was divide by one
+}
diff --git a/part_4/4.8/1.go b/part_4/4.8/1.go
new file mode 100644
index 0000000..0c231e8
--- /dev/null
+++ b/part_4/4.8/1.go
@@ -0,0 +1,62 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+type DivError struct {
+	Numerator   int
+	Denominator int
+	Msg         string
+}
+
+func (d *DivError) Error() string {
+	return d.Msg
+}
+
+func div(a, b int) (int, error) {
+	if b == 0 {
+		return 0, &DivError{
+			Numerator:   a,
+			Denominator: b,
+			Msg:         fmt.Sprintf("Сan't divide '%v' by zero", a),
+		}
+	}
+	if b == 1 {
+		return a, &DivError{
+			Numerator:   a,
+			Denominator: b,
+			Msg:         "Divide by one",
+		}
+	}
+	return a / b, nil
+}
+
+func printResult(result int, err error) {
+	if err != nil {
+		var myDivError *DivError
+		switch {
+		case errors.As(err, &myDivError):
+			fmt.Printf("Numerator: %d, Denominator: %d, Error: %s\n",
+				myDivError.Numerator, myDivError.Denominator, myDivError.Msg)
+			if myDivError.Denominator == 1 {
+				fmt.Printf("result = %d, but was %v\n",
+					myDivError.Numerator, myDivError.Msg)
+			}
+		default:
+			fmt.Printf("unexpected error: %v\n", err)
+		}
+
+	} else {
+		fmt.Println(result)
+	}
+}
+
+func main() {
+	printResult(div(10, 2)) // 5
+	printResult(div(4, 0))  // Numerator: 4, Denominator: 0, Error: Сan't divide '4' by zero
+	printResult(div(12, 1))
+	// Numerator: 12, Denominator: 1, Error: Divide by one
+	// result = 12, but was divide by one
+}
diff --git a/part_4/4.9/1.go b/part_4/4.9/1.go
new file mode 100644
index 0000000..dd77ecf
--- /dev/null
+++ b/part_4/4.9/1.go
@@ -0,0 +1,122 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+)
+
+type User struct {
+	ID   uint
+	Name string
+	Age  uint8
+}
+
+type UserDB struct {
+	users []User
+}
+
+func (db *UserDB) FindUserWithID(id uint) (*User, error) {
+	for _, it := range db.users {
+		if it.ID == id {
+			return &it, nil
+		}
+	}
+	return nil, fmt.Errorf("User with id=%v not found", id)
+}
+
+func (db *UserDB) SetUserAge(id uint, age uint8) error {
+	for _, it := range db.users {
+		if it.ID == id {
+			it.Age = age
+			return nil
+		}
+	}
+	return fmt.Errorf("User with id=%v not found", id)
+}
+
+func (db *UserDB) AddUser(user User) error {
+	for _, it := range db.users {
+		if it.ID == user.ID {
+			return fmt.Errorf("User with id=%v already exist", user.ID)
+		}
+	}
+	db.users = append(db.users, user)
+	return nil
+}
+
+func (db *UserDB) DeleteUserWithName(name string) error {
+	index := -1
+	for idx, it := range db.users {
+		if it.Name == name {
+			index = idx
+			break
+		}
+	}
+	if index < 0 {
+		return fmt.Errorf("User %s not found", name)
+	}
+	db.users = append(db.users[:index], db.users[index+1:]...)
+	return nil
+}
+
+// функции для работы с БД и организации цепочек ошибок
+func findUserWithID(db *UserDB, id uint) (*User, error) {
+	user, err := db.FindUserWithID(id)
+	if err != nil {
+		// вернется ошибка из 2-х вложений
+		return nil, fmt.Errorf("DataBase error: %w", err)
+	}
+	return user, nil
+}
+
+func setUserAge(db *UserDB, id uint, age uint8) error {
+	err := db.SetUserAge(id, age)
+	if err != nil {
+		// вернется ошибка из 2-х вложений
+		return fmt.Errorf("DataBase user data error: %w", err)
+	}
+	return nil
+}
+
+func addUser(db *UserDB, user User) error {
+	err := db.AddUser(user)
+	if err != nil {
+		// вернется ошибка из 2-х вложений
+		return fmt.Errorf("Add user error: %w", err)
+	}
+	return nil
+}
+
+func main() {
+	dbUsers := UserDB{
+		[]User{
+			{2, "Alex", 28},
+			{1, "Max", 23},
+			{10, "German", 35},
+			{6, "Oleg", 19},
+		},
+	}
+
+	user, err := findUserWithID(&dbUsers, 2)
+	if err != nil {
+		fmt.Println(err)
+		// распаковка трассировки ошибок
+		fmt.Println(errors.Unwrap(err))
+	}
+	fmt.Printf("%+v\n", user) // &{ID:2 Name:Alex Age:28}
+
+	user, err = findUserWithID(&dbUsers, 12)
+	if err != nil {
+		fmt.Println(err) // DataBase error: User with id=12 not found
+		// распаковка трассировки ошибок
+		fmt.Println(errors.Unwrap(err)) // User with id=12 not found
+	}
+	fmt.Printf("%+v\n", user) // <nil>
+
+	newErr := addUser(&dbUsers, User{6, "Li", 45})
+	if newErr != nil {
+		fmt.Println(newErr) // Add user error: User with id=6 already exist
+		// распаковка трассировки ошибок
+		fmt.Println(errors.Unwrap(newErr)) // User with id=6 already exist
+	}
+}