add chapter 4

chapter4/const/const.go

@@ -0,0 +1,18 @@
+package main
+
+import "fmt"
+
+// объявление константы с типом
+const TriangleSides int = 3
+
+// объявление константы без типа
+const SquareSides = 4
+
+/* константам переназначить значение невозможно
+const PentagonSides = 5
+PentagonSides = 6 // error
+*/
+
+func main() {
+	fmt.Println(TriangleSides, SquareSides)
+}

chapter4/const/dates/dates.go

@@ -0,0 +1,11 @@
+package dates
+
+const DaysInWeek = 7
+
+func WeeksToDays(weeks int) int {
+	return weeks * DaysInWeek
+}
+
+func DaysToWeek(days int) float64 {
+	return float64(days) / float64(DaysInWeek)
+}

chapter4/const/planner/main.go

@@ -0,0 +1,12 @@
+package main
+
+import (
+	"fmt"
+	"golang-book/head-first-go/chapter4/const/dates"
+)
+
+func main() {
+	days := 3
+	fmt.Println("Your appointment is", days, "days")
+	fmt.Println("with a follow-up in", days+dates.DaysInWeek, "days")
+}

chapter4/greeting/greeting.go

@@ -0,0 +1,11 @@
+package greeting
+
+import "fmt"
+
+func Hello() {
+	fmt.Println("Hello!")
+}
+
+func Hi() {
+	fmt.Println("Hi!")
+}

chapter4/hi/main.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"fmt"
+	"golang-book/head-first-go/chapter4/greeting"
+)
+
+func main() {
+	greeting.Hello()
+	greeting.Hi()
+
+	slc := []string{"hello", "world"}
+	fmt.Printf("%s %T %T", slc[0], slc, true)
+}

chapter4/keyboard/keyboard.go

@@ -0,0 +1,23 @@
+package keyboard
+
+import (
+	"bufio"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func GetFloat() (float64, error) {
+	reader := bufio.NewReader(os.Stdin)
+	input, err := reader.ReadString('\n')
+	if err != nil {
+		return 0, err
+	}
+
+	input = strings.TrimSpace(input)
+	number, err := strconv.ParseFloat(input, 64)
+	if err != nil {
+		return 0, err
+	}
+	return number, nil
+}

chapter4/passfail/pass_fail.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"fmt"
+	"golang-book/head-first-go/chapter4/keyboard"
+	"log"
+)
+
+func main() {
+	fmt.Print("Enter a grade: ")
+	grade, err := keyboard.GetFloat()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	var status string
+	if grade >= 60 {
+		status = "passing"
+	} else {
+		status = "failing"
+	}
+	fmt.Println("A grade of", grade, "is", status)
+}

chapter4/tocelsius/tocelsius.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"fmt"
+	"golang-book/head-first-go/chapter4/keyboard"
+	"log"
+)
+
+func main() {
+	fmt.Print("Enter a temperature in Farenheit: ")
+	farenheit, err := keyboard.GetFloat()
+	if err != nil {
+		log.Fatal(err)
+	}
+	celsius := (farenheit - 32) * 5 / 9
+	fmt.Printf("%0.2f degrees Celsius\n", celsius)
+}