with Ada.Text_Io, Ada.Integer_Text_Io;
use Ada.Text_Io, Ada.Integer_Text_Io;

procedure Ex01a is
   -- Constantes pour le test, ne fait pas partie de la réponse
   A : constant Natural := 1;
   B : constant Natural := 2;
   C : constant Natural := 3;
   D : constant Natural := 4;

   X : Natural := A;
   Y : Natural := B;
   Z : Natural := C;
   T : Natural := D;

   Tmp : Natural; -- variable intermédiaire
begin
   Put("X = ");   Put(X, 1);   Put("  Y = "); Put(Y, 1);
   Put("  Z = "); Put(Z, 1);   Put("  T = "); Put(T, 1); New_Line;

   --- Début algo ---
   Tmp := X;
   X := Y;
   Y := T;
   T := Z;
   Z := Tmp;
   --- Fin   algo ---

   Put("X = ");   Put(X, 1);   Put("  Y = "); Put(Y, 1);
   Put("  Z = "); Put(Z, 1);   Put("  T = "); Put(T, 1);
end;