new files

Task/Caesar-cipher/Ada/caesar-cipher.ada

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+with Ada.Text_IO;
+
+procedure Caesar is
+
+   type M26 is mod 26;
+
+   function To_M26(C: Character; Offset: Character) return M26 is
+   begin
+      return M26(Character'Pos(C)-Character'Pos(Offset));
+   end To_M26;
+
+   function To_Character(Value:   in  M26; Offset: Character)
+                        return Character is
+   begin
+      return Character'Val(Integer(Value)+Character'Pos(Offset));
+   end To_Character;
+
+   function Encrypt (Plain: String; Key: M26) return String is
+      Ciph: String(Plain'Range);
+
+   begin
+      for I in Plain'Range loop
+         case Plain(I) is
+            when 'A' .. 'Z' =>
+               Ciph(I) := To_Character(To_M26(Plain(I), 'A')+Key, 'A');
+            when 'a' .. 'z' =>
+               Ciph(I) := To_Character(To_M26(Plain(I), 'a')+Key, 'a');
+            when others =>
+               Ciph(I) := Plain(I);
+         end case;
+      end loop;
+      return Ciph;
+   end Encrypt;
+
+   Text:  String := Ada.Text_IO.Get_Line;
+   Key: M26 := 3; -- Default key from "Commentarii de Bello Gallico"
+
+begin -- Caesar main program
+
+   Ada.Text_IO.Put_Line("Plaintext ------------>" & Text);
+   Text := Encrypt(Text, Key);
+   Ada.Text_IO.Put_Line("Ciphertext ----------->" & Text);
+   Ada.Text_IO.Put_Line("Decrypted Ciphertext ->" & Encrypt(Text, -Key));
+
+end Caesar;