Add activities 4.04 & 4.05 & exercices 4.13-4.17

chapter_04/activity_4.04/main.go

@@ -0,0 +1,13 @@
+package main
+
+import "fmt"
+
+func main() {
+
+  days := []string{
+    "Monday", "Tuesday", "Wednesday", "Thursday",
+    "Friday", "Saturday", "Sunday"}
+  days = append(days[len(days)-1:], days[:len(days)-1]...)
+  fmt.Println(days)
+
+}

chapter_04/activity_4.05/main.go

@@ -0,0 +1,11 @@
+package main
+
+import "fmt"
+
+func main() {
+
+  s := []string{"Good", "Good", "Bad", "Good", "Good"}
+  s = append(s[:2], s[3:]...)
+  fmt.Println(s)
+
+}

chapter_04/exercise_4.13/main.go

@@ -0,0 +1,21 @@
+package main
+
+import "fmt"
+
+func getUsers() map[string]string {
+
+  users := map[string]string{
+    "305": "Sue",
+    "204": "Bob",
+    "631": "Jake",
+  }
+  users["073"] = "Tracy"
+  return users
+
+}
+
+func main() {
+
+  fmt.Println("Users:", getUsers())
+
+}

chapter_04/exercise_4.14/main.go

@@ -0,0 +1,47 @@
+package main
+
+import (
+  "fmt"
+  "os"
+)
+
+func getUsers() map[string]string {
+
+  return map[string]string{
+    "305": "Sue",
+    "204": "Bob",
+    "631": "Jake",
+    "073": "Tracy",
+  }
+
+}
+
+func getUser(id string) (string, bool) {
+
+  users := getUsers()
+  user, exists := users[id]
+  return user, exists
+
+}
+
+func main() {
+
+  if len(os.Args) != 2 {
+    fmt.Println("User ID not passed")
+    os.Exit(1)
+  }
+
+  userID := os.Args[1]
+  name, exists := getUser(userID)
+
+  if !exists {
+    fmt.Printf("Passed user ID (%v) not found.\nUsers: \n", userID)
+    for key, value := range getUsers() {
+      fmt.Println("   ID:", key, "Name:", value)
+    }
+    os.Exit(1)
+  }
+
+  fmt.Println("Name:", name)
+
+}

chapter_04/exercise_4.15/main.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+  "fmt"
+  "os"
+)
+
+var users = map[string]string{
+  "305": "Sue",
+  "204": "Bob",
+  "631": "Jake",
+  "073": "Tracy",
+}
+
+func deleteUser(id string) {
+
+  delete(users, id)
+
+}
+
+func main() {
+
+  if len(os.Args) != 2 {
+    fmt.Println("User ID not passed")
+    os.Exit(1)
+  }
+
+  userID := os.Args[1]
+  deleteUser(userID)
+  fmt.Println("Users:", users)
+
+}

chapter_04/exercise_4.16/main.go

@@ -0,0 +1,24 @@
+package main
+
+import "fmt"
+
+type id string
+
+func getIDs() (id, id, id) {
+
+  var id1 id
+  var id2 id = "1234-5678"
+  var id3 id
+  id3 = "1234-5678"
+  return id1, id2, id3
+
+}
+
+func main() {
+
+  id1, id2, id3 := getIDs()
+  fmt.Println("id1 == id2:       ", id1 == id2)
+  fmt.Println("id2 == id3:       ", id2 == id3)
+  fmt.Println("id2 == \"1234-5678\"", string(id2) == "1234-5678")
+
+}

chapter_04/exercise_4.17/main.go

@@ -0,0 +1,51 @@
+package main
+
+import "fmt"
+
+type user struct {
+  name    string
+  age     int
+  balance float64
+  member  bool
+}
+
+func getUsers() []user {
+
+  u1 := user{
+    name:    "Tracy",
+    age:     51,
+    balance: 98.43,
+    member:  true,
+  }
+
+  u2 := user{
+    age:  19,
+    name: "Nick",
+  }
+
+  u3 := user{
+    "Bob",
+    25,
+    0,
+    false,
+  }
+
+  var u4 user
+  u4.name = "Sue"
+  u4.age = 31
+  u4.member = true
+  u4.balance = 17.09
+
+  return []user{u1, u2, u3, u4}
+
+}
+
+func main() {
+
+  users := getUsers()
+
+  for i := 0; i < len(users); i++ {
+    fmt.Printf("%v: %#v\n", i, users[i])
+  }
+
+}