diff --git a/lib/cash_register.py b/lib/cash_register.py
index e869386..8991b5f 100644
--- a/lib/cash_register.py
+++ b/lib/cash_register.py
@@ -1,4 +1,52 @@
-#!/usr/bin/env python3
+
 
 class CashRegister:
-  pass
+    def __init__(self, discount=0):
+        
+        if isinstance(discount, int) and 0 <= discount <= 100:
+            self.discount = discount
+        else:
+            print("Not valid discount")
+            self.discount = 0
+
+        self.total = 0
+        self.items = []
+        self.previous_transactions = []
+
+    def add_item(self, item, price, quantity=1):
+       
+        self.total += price * quantity
+        for _ in range(quantity):
+            self.items.append(item)
+        self.previous_transactions.append({
+            'item': item,
+            'price': price,
+            'quantity': quantity
+        })
+
+    def apply_discount(self):
+       
+        if self.discount == 0:
+            print("There is no discount to apply.")
+            return
+        
+        self.total = self.total * (100 - self.discount) / 100
+        
+        if float(self.total).is_integer():
+            total_str = str(int(self.total))
+        else:
+            total_str = str(self.total)
+        print(f"After the discount, the total comes to ${total_str}.")
+
+    def void_last_transaction(self):
+       
+        if not self.previous_transactions:
+            print("No transaction to void.")
+            return
+        last = self.previous_transactions.pop()
+       
+        self.total -= last['price'] * last['quantity']
+       
+        for _ in range(last['quantity']):
+            if last['item'] in self.items:
+                self.items.remove(last['item'])
\ No newline at end of file