Adding of a new exercise printrot.

The goal: printing the alphabet from a chosen letter and going around all the letters.

go/tests/prog/printrot_prog/main.go

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+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func printAnswer(letter rune) {
+	answer := []rune{}
+	for i := letter; i <= 'z'; i++ {
+		answer = append(answer, i)
+	}
+	for j := 'a'; j < letter; j++ {
+		answer = append(answer, j)
+	}
+	fmt.Println(string(answer))
+}
+
+func main() {
+	if len(os.Args) == 2 {
+		letter := os.Args[1]
+		if len(letter) == 1 {
+			letterConverted := []rune(letter)
+			if letterConverted[0] >= 'a' && letterConverted[0] <= 'z' {
+				printAnswer(letterConverted[0])
+			}
+		} else {
+			fmt.Println()
+		}
+	} else {
+		fmt.Println()
+	}
+}

go/tests/prog/printrot_test/main.go

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+package main
+
+import (
+	"lib"
+	"strings"
+)
+
+func main() {
+	table := string{}
+	table = append(table, "A")
+	table = append(table, "a")
+	table = append(table, "b")
+	table = append(table, "c")
+	table = append(table, "d")
+	table = append(table, "e")
+	table = append(table, "f")
+	table = append(table, "g")
+	table = append(table, "h")
+	table = append(table, "i")
+	table = append(table, "j")
+	table = append(table, "k")
+	table = append(table, "l")
+	table = append(table, "m")
+	table = append(table, "n")
+	table = append(table, "o")
+	table = append(table, "p")
+	table = append(table, "q")
+	table = append(table, "r")
+	table = append(table, "s")
+	table = append(table, "t")
+	table = append(table, "u")
+	table = append(table, "v")
+	table = append(table, "w")
+	table = append(table, "x")
+	table = append(table, "y")
+	table = append(table, "z")
+	table = append(table, "Z")
+	table = append(table, "2 arguments")
+	table = append(table, "4 arguments so invalid")
+
+	for _, s := range table {
+		lib.ChallengeMain("printrot", strings.Fields(s)...)
+	}
+}

subjects/printrot/README.md

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+## printrot
+
+### Instructions
+
+Write a program that takes a lower case letter and goes around in order to display the whole alphabet starting from
+this letter on a single line.
+
+A line is a sequence of characters preceding the [end of line](https://en.wikipedia.org/wiki/Newline) character (`'\n'`).
+
+If the input is invalid the program prints a newline (`'\n'`).
+
+### Usage
+
+```console
+student@ubuntu:~/[[ROOT]]/test$ go build
+student@ubuntu:~/[[ROOT]]/test$ ./test "abc"
+
+student@ubuntu:~/[[ROOT]]/test$ ./test "a"
+abcdefghijklmnopqrstuvwxyz
+student@ubuntu:~/[[ROOT]]/test$ ./test "g"
+ghijklmnopqrstuvwxyzabcdef
+student@ubuntu:~/[[ROOT]]/test$ ./test "a" "a"
+
+student@ubuntu:~/[[ROOT]]/test$ ./test "A"
+
+student@ubuntu:~/[[ROOT]]/test$
+```