Enhanced Caesar Cipher: Secure & User-Friendly Encryption

README.md

@@ -1,3 +1,4 @@
+
 # PRODIGY_CS_01
 
 # Caesar Cipher 🔐

caesar_cipher.py

@@ -1,34 +1,62 @@
+
+
 alphabet = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u',
             'v', 'w', 'x', 'y', 'z']
 
-
 def caesar(original_text, shift_amount, encode_or_decode):
     output_text = ""
     if encode_or_decode == "decode":
         shift_amount *= -1
+    elif encode_or_decode != "encode":
+        print("Invalid direction. Please use 'encode' or 'decode'.")
+        return
 
-    for letter in original_text:
+    shift_amount = shift_amount % len(alphabet)  # Handle large shifts
 
-        if letter not in alphabet:
+    for letter in original_text:
+        if letter.lower() not in alphabet:
             output_text += letter
         else:
-            shifted_position = alphabet.index(letter) + shift_amount
+            # Preserve original case
+            is_upper = letter.isupper()
+            letter_lower = letter.lower()
+
+            shifted_position = alphabet.index(letter_lower) + shift_amount
             shifted_position %= len(alphabet)
-            output_text += alphabet[shifted_position]
-    print(f"Here is the {encode_or_decode}d result: {output_text}")
+            new_letter = alphabet[shifted_position]
+
+            output_text += new_letter.upper() if is_upper else new_letter
+
+    print(f"\nHere is the {encode_or_decode}d result: {output_text}\n")
+
+def get_valid_shift():
+    while True:
+        try:
+            shift = int(input("Type the shift number (0-25 recommended): "))
+            return shift
+        except ValueError:
+            print("Please enter a valid integer.")
 
+def main():
+    to_continue = True
+    print("Welcome to the Caesar Cipher Program!")
 
-to_continue = True
+    while to_continue:
+        print("\n" + "="*40)
+        direction = input("Type 'encode' to encrypt, type 'decode' to decrypt:\n").lower()
+        if direction not in ['encode', 'decode']:
+            print("Invalid choice. Please try again.")
+            continue
 
-while to_continue:
+        text = input("Type your message:\n")
+        shift = get_valid_shift()
 
-    direction = input("Type 'encode' to encrypt, type 'decode' to decrypt:\n").lower()
-    text = input("Type your message:\n").lower()
-    shift = int(input("Type the shift number:\n"))
+        caesar(text, shift, direction)
 
-    caesar(text,shift,direction)
+        restart = input("\nType 'yes' if you want to go again. Otherwise, type 'no':\n").lower()
+        if restart != 'yes':
+            to_continue = False
+            print("\nThank you for using the Caesar Cipher Program!")
 
-    restart = input("Type 'yes' if you want to go again. Otherwise, type 'no'.\n").lower()
-    if restart == "no":
-        to_continue = False
-        print("Thank You!")
+if __name__ == "__main__":
+    main()