Added C++ Implementation

cpp/vigenere.cpp

@@ -0,0 +1,65 @@
+#include <iostream>
+#include <string>
+#include <cctype>
+using namespace std;
+
+class VigenereCipher {
+public:
+    // Encryption function to encrypt the plaintext using the key
+    string encrypt(const string &plaintext, const string &key) {
+        string ciphertext;
+        int keyIndex = 0;
+        int keyLength = key.length();
+
+        for (char ch : plaintext) {
+            if (isalpha(ch)) {
+                char base = isupper(ch) ? 'A' : 'a';
+                char keyChar = toupper(key[keyIndex % keyLength]) - 'A';
+                char encryptedChar = (ch - base + keyChar) % 26 + base;
+                ciphertext += encryptedChar;
+                keyIndex++;
+            } else {
+                ciphertext += ch; // Non-albhabetic character will be added as is it
+            }
+        }
+        return ciphertext;
+    }
+
+    // Decryption function the ciphertext using the key
+    string decrypt(const string &ciphertext, const string &key) {
+        string plaintext;
+        int keyIndex = 0;
+        int keyLength = key.length();
+
+        for (char ch : ciphertext) {
+            if (isalpha(ch)) {
+                char base = isupper(ch) ? 'A' : 'a';
+                char keyChar = toupper(key[keyIndex % keyLength]) - 'A';
+                char decryptedChar = (ch - base - keyChar + 26) % 26 + base;
+                plaintext += decryptedChar;
+                keyIndex++;
+            } else {
+                plaintext += ch; // Non-alphabetic character will be added as it is.
+            }
+        }
+        return plaintext;
+    }
+};
+
+int main() {
+    VigenereCipher vc;
+    string plaintext, key;
+
+    cout << "Enter plaintext: ";
+    getline(cin, plaintext);
+    cout << "Enter key: ";
+    getline(cin, key);
+
+    string encrypted = vc.encrypt(plaintext, key);
+    cout << "Encrypted text: " << encrypted << endl;
+
+    string decrypted = vc.decrypt(encrypted, key);
+    cout << "Decrypted text: " << decrypted << endl;
+
+    return 0;
+}