#include #include

using namespace std;

string encrypt(string message, int key) { string encrypted = "";

 for (char ch : message) {
     if (isalpha(ch)) {
         char base = isupper(ch) ? 'A' : 'a';
         encrypted += (ch - base + key) % 26 + base;
     } else {
         encrypted += ch; 
     }
 }

 return encrypted;

}

string decrypt(string message, int key) { return encrypt(message, 26 - key); }

int main() { string message; int key;

 cout << "Enter a message to encrypt: ";
 getline(cin, message);

 cout << "Enter a key (1-25): ";
 cin >> key;

 
 if (key < 1 || key > 25) {
     cout << "Invalid key. Must be between 1 and 25." << endl;
     return 1;
 }

 string encrypted = encrypt(message, key);
 string decrypted = decrypt(encrypted, key);

 cout << "\nEncrypted message: " << encrypted << endl;
 cout << "Decrypted message: " << decrypted << endl;

 return 0;