modulo implementation, uppercase compatibility, corrected caesar spel…

…ling (；^＿^)

README.md

@@ -1,9 +1,9 @@
-# Julius Ceasar's Substitution Cipher!
+# Julius Caesar's Substitution Cipher!
 Enter an integer (key) to left shift the normal alphabet by that number of positions.  
 Then, enter a message to encrypt using your new cipher alphabet.  
 🔥 FYI a key of 13 is effectively ROT-13.  
 #### web app version
-https://calebdanderson.net/ceasar-cipher.html
+~~https://calebdanderson.net/ceasar-cipher.html~~
 #### more info
 https://en.wikipedia.org/wiki/Caesar_cipher  
 https://en.wikipedia.org/wiki/ROT13

ceasar-cipher.cpp → caesar-cipher.cpp

@@ -1,6 +1,9 @@
-#include "ceasar-cipher.h"
+#include "caesar-cipher.h"
 #include <iostream>
 
+// https://www.tutorialspoint.com/cplusplus-program-to-implement-caesar-cypher
+// https://www.asciihex.com/
+
 using namespace std;
 
 void encryption(const string &plainAlpha, char &discard) {
@@ -24,7 +27,7 @@ void encryption(const string &plainAlpha, char &discard) {
     // shift alphabet [key] letters to the left
     cipherAlphabet = cipherAlpha(key, plainAlpha);
     // encrypt the message using the cipher alphabet
-    cipherText = cipherMessage(cipherAlphabet, plainAlpha, message);
+    cipherText = cipherMessage(message, key);
 
     cout << "\nPlaintext: " << message << endl;
     cout << "Plain alphabet:  " << plainAlpha << "." << endl;
@@ -53,42 +56,43 @@ void decryption(const string &plainAlpha, char &discard) {
     cout << "Plain alphabet:  " << plainAlpha << "." << endl;
     cout << "Cipher alphabet: " << cipherAlpha(key, plainAlpha) << "; Shifted [" << key << "] place(s) to the left." << endl;
     // display decrypted message
-    cout << "Plaintext: " << decrypt(cipherText, plainAlpha, key) << endl << endl;
+    cout << "Plaintext: " << decrypt(cipherText, key) << endl << endl;
 }
 
 string cipherAlpha(int &key, const string &plainAlpha) {
-    string cipherAlpha = plainAlpha;                // cypherAlpha same size as plainAlpha
-    int p = 0;                                      // wrap around variable
-    for (int i = 0; i < plainAlpha.size(); i++) {
-        if (i + key >= plainAlpha.size()) {         // wrap around when i + key >= 26
-            cipherAlpha[i] = plainAlpha[p];         // shift cipherAlpha
-            p++;
-        } else {
-            cipherAlpha[i] = plainAlpha[i + key];   // shift cipherAlpha
-        }
+    string cipherAlpha;
+    for (char c : plainAlpha) {
+        cipherAlpha += static_cast<char>((c + key - 65) % 26 + 65);
     }
     return cipherAlpha;
 }
 
-string cipherMessage(const string &cipherAlpha, const string &plainAlpha, const string &message) {
-    string cipherText = message;                        // cipherText same size as message
-    for (int i = 0; i < cipherAlpha.size(); i++) {      // loop over all letters in the alphabet
-        for (int j = 0; j < message.size(); j++) {      // loop over all letters in the message
-            if (plainAlpha[i] == message[j])
-                cipherText[j] = cipherAlpha[i];         // replace each plainAlpha letter in the message with the cipherAlpha letter
-        }
+string cipherMessage(const string &message, int &key) {
+    string cipherText;
+    for (char c : message) {
+        if (c >= 65 && c <= 122)
+            if (isupper(c)) {
+                cipherText += static_cast<char>((c + key - 65) % 26 + 65);
+            } else {
+                cipherText += static_cast<char>((c + key - 97) % 26 + 97);
+            }
+        else
+            cipherText += c;
     }
     return cipherText;
 }
 
-string decrypt(const string &cipherText, const string &plainAlpha, int &key) {
-    string plainText = cipherText;                                  // plainText same size as cipherText
-    string cipherAlphabet = cipherAlpha(key, plainAlpha);       // generate cipherAlphabet
-    for (int i = 0; i < cipherAlphabet.size(); i++) {               // loop over all letters in alphabet
-        for (int j = 0; j < cipherText.size(); j++) {               // loop over all letters in the cipherText
-            if (cipherAlphabet[i] == cipherText[j])
-                plainText[j] = plainAlpha[i];                       // replace each cipherAlpha letter in the message with the plainAlpha letter
-        }
+string decrypt(const string &cipherText, int &key) {
+    string plainText;
+    for (char c : cipherText) {
+        if (c >= 65 && c <= 122)
+            if (isupper(c)) {
+                plainText += static_cast<char>((c - key - 65 % 26 + 26) % 26 + 65);
+            } else {
+                plainText += static_cast<char>((c - key - 97 % 26 + 26) % 26 + 97);
+            }
+        else
+            plainText += c;
     }
     return plainText;
-}
+}

ceasar-cipher.h → caesar-cipher.h

@@ -1,7 +1,7 @@
-#ifndef CEASAR_CIPHER_CEASAR_CIPHER_H
-#define CEASAR_CIPHER_CEASAR_CIPHER_H
+#ifndef CAESAR_CIPHER_CAESAR_CIPHER_H
+#define CAESAR_CIPHER_CAESAR_CIPHER_H
 
-#endif //CEASAR_CIPHER_CEASAR_CIPHER_H
+#endif //CAESAR_CIPHER_CAESAR_CIPHER_H
 
 #include <iostream>
 using namespace std;
@@ -20,12 +20,10 @@ string cipherAlpha(int&, const string&);
 // Function to generate cipher alphabet.
 // Postcondition: const string shifted left by int positions
 
-string cipherMessage(const string&, const string&, const string&);
+string cipherMessage(const string&, int&);
 // Function to encrypt the message
-// Postcondition: string A (plain alphabet), compared to string B (cipher alphabet)
-//                string C (message) enciphered
+// Postcondition: string message shifted left by int positions
 
-string decrypt(const string&, const string&, int&);
+string decrypt(const string&, int&);
 // Function to decrypt the message
-// Postcondition: string A (ciphertext), compared to string B (plain alphabet)
-//                deciphered (shifted) by int positions
+// Postcondition: string ciphertext shifted back to the right by int positions

main.cpp

@@ -1,15 +1,16 @@
 #include <iostream>
-#include "ceasar-cipher.h"
+#include "caesar-cipher.h"
+
 using namespace std;
 
 int main() {
-    cout << "\nWelcome to Julius Ceasar's Shift Cipher!"
+    cout << "\nWelcome to Julius Caesar's Shift Cipher!"
             "\nEnter an integer to shift the normal alphabet left by that number of positions." << endl;
     cout << "Then, enter a message that will be encrypted using your cipher alphabet." << endl;
     cout << "https://en.wikipedia.org/wiki/Caesar_cipher\n" << endl;
 
     int option = -1;
-    string plainAlpha = "abcdefghijklmnopqrstuvwxyz";
+    string plainAlpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
     char discard;
 
     while (option != 0) {