add: switch statement exercises

12-switch/exercises/04-string-manipulator/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+// ---------------------------------------------------------
+// STORY
+//  You want to write a program that will manipulate the
+//  given strings to uppercase, lowercase, and title case.
+//
+// EXERCISE: String Manipulator
+//
+//  1. Get the operation as the first argument.
+//
+//  2. Get the string to be manipulated as the 2nd argument.
+//
+// HINT
+//  You can find the manipulation functions in the strings
+//  package Go documentation (ToLower, ToUpper, Title).
+//
+// EXPECTED OUTPUT
+//
+//  go run main.go
+//    [command] [string]
+//
+//    Available commands: lower, upper and title
+//
+//  go run main.go lower 'OMG!'
+//    omg!
+//
+//  go run main.go upper 'omg!'
+//    OMG!
+//
+//  go run main.go title "mr. charles darwin"
+//    Mr. Charles Darwin
+//
+//  go run main.go genius "mr. charles darwin"
+//    Unknown command: "genius"
+// ---------------------------------------------------------
+
+func main() {
+
+}

12-switch/exercises/04-string-manipulator/solution/main.go

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+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+const usage = `[command] [string]
+
+Available commands: lower, upper and title`
+
+func main() {
+	args := os.Args
+	if len(args) != 3 {
+		fmt.Println(usage)
+		return
+	}
+
+	cmd, str := args[1], args[2]
+	switch cmd {
+	case "lower":
+		fmt.Println(strings.ToLower(str))
+	case "upper":
+		fmt.Println(strings.ToUpper(str))
+	case "title":
+		fmt.Println(strings.Title(str))
+	default:
+		fmt.Printf("Unknown command: %q\n", cmd)
+	}
+}