diff --git a/expression.py b/expression.py
index 7a37915..260e2c4 100644
--- a/expression.py
+++ b/expression.py
@@ -11,21 +11,27 @@ class Expression:
         """renvoie la valeur de l'expression"""
         if self.racine == "+":
             return self.gauche.evalue() + self.droit.evalue()
+        if self.racine == "-":
+            return self.gauche.evalue() - self.droit.evalue()
         if self.racine == "*":
             return self.gauche.evalue() * self.droit.evalue()
+        if self.racine == "/":
+            return self.gauche.evalue() / self.droit.evalue()
         
-        return self.racine
+        
+        return int(self.racine)
    
     def __str__(self):
         """affiche l'expression"""
         #temporaire
-        if self.racine in ["+","*"]:
-            return "(" + str(self.gauche) + ")" + self.racine + "(" + str(self.droit) + ")"
+        if self.racine in ["+", "*"]:
+            return  "(" + str(self.gauche)  + self.racine + str(self.droit) + ")"
         
         return str(self.racine)
     
     
 def npi2tree(liste_en_npi):
+    """conversion d'une liste en NPI en un arbre"""
     pile_expr = Pile()
     for element in liste_en_npi:
         if element in ["+", "*"]:
diff --git a/interface.py b/interface.py
new file mode 100644
index 0000000..81d9924
--- /dev/null
+++ b/interface.py
@@ -0,0 +1,46 @@
+import tkinter as tk
+from expression import *
+
+class Interface(tk.Frame):
+    def __init__(self, master):
+        self.master = master
+        tk.Frame.__init__(self, master)
+        
+        self.saisie_expression = tk.Entry(self.master)
+        self.saisie_expression.grid(row=0, column=0)
+        self.saisie_expression.bind("<Return>", lambda e : self.evaluer())
+        self.saisie_expression.bind("<KP_Enter>", lambda e : self.evaluer())
+        
+        
+        btn_calculer = tk.Button(self.master, text='évaluer', command=self.evaluer)
+        btn_calculer.grid(row=0, column=2)
+        
+        self.affichage_expression = tk.Label(self.master)
+        self.affichage_expression.grid(row=1, column=0)
+        
+        tk.Label(self.master, text = "=").grid(row=1, column=1)
+        
+        self.res = tk.Label(self.master)
+        self.res.grid(row=1, column=2)
+
+        
+    def evaluer(self):
+        lst_expr = self.saisie_expression.get().split()
+        try:
+            arbre_expr = npi2tree(lst_expr)
+            self.affichage_expression.config(text = str(arbre_expr))
+            self.res.config(text = arbre_expr.evalue())
+        except IndexError:
+            self.affichage_expression.config(text = "Erreur")
+            self.res.config(text = "Erreur")
+        
+        
+        
+
+    
+if __name__ == "__main__":
+    root = tk.Tk()
+    root.title("Calculatrice")
+    root.geometry("350x500")
+    hello_frame = Interface(root)
+    hello_frame.mainloop()
\ No newline at end of file