Caesar Cipher in C and C++ [Encryption & Decryption]

Caesar Cipher in C and C++ [Encryption & Decryption]:-

Get program for caesar cipher in C and C++ for encryption and decryption.

What is Caesar Cipher?

It is one of the simplest encryption technique in which each character in plain text is replaced by a character some fixed number of positions down to it.

For example, if key is 3 then we have to replace character by another character that is 3 position down to it. Like A will be replaced by D, C will be replaced by F and so on.

For decryption just follow the reverse of encryption process.

Below I have shared program to implement caesar cipher in C and C++.

Also Read: Vigenere Cipher in C and C++

Program for Caesar Cipher in C
Encryption


#include<stdio.h>

int main()
{
char message[100], ch;
int i, key;

printf("Enter a message to encrypt: ");
gets(message);
printf("Enter key: ");
scanf("%d", &key);

for(i = 0; message[i] != '\0'; ++i){
ch = message[i];

if(ch >= 'a' && ch <= 'z'){
ch = ch + key;

if(ch > 'z'){
ch = ch - 'z' + 'a' - 1;
}

message[i] = ch;
}
else if(ch >= 'A' && ch <= 'Z'){
ch = ch + key;

if(ch > 'Z'){
ch = ch - 'Z' + 'A' - 1;
}

message[i] = ch;
}
}

printf("Encrypted message: %s", message);

return 0;
}
Output

Enter a message to encrypt: axzd
Enter key: 4
Encrypted message: ebdh


Decryption


#include<stdio.h>

int main()
{
char message[100], ch;
int i, key;

printf("Enter a message to decrypt: ");
gets(message);
printf("Enter key: ");
scanf("%d", &key);

for(i = 0; message[i] != '\0'; ++i){
ch = message[i];

if(ch >= 'a' && ch <= 'z'){
ch = ch - key;

if(ch < 'a'){
ch = ch + 'z' - 'a' + 1;
}

message[i] = ch;
}
else if(ch >= 'A' && ch <= 'Z'){
ch = ch - key;

if(ch < 'A'){
ch = ch + 'Z' - 'A' + 1;
}

message[i] = ch;
}
}

printf("Decrypted message: %s", message);

return 0;
}
Output

Enter a message to decrypt: ebdh
Enter key: 4
Decrypted message: axzd



Program for Caesar Cipher in C++
Encryption


#include<iostream>

using namespace std;

int main()
{
char message[100], ch;
int i, key;

cout << "Enter a message to encrypt: ";
cin.getline(message, 100);
cout << "Enter key: ";
cin >> key;

for(i = 0; message[i] != '\0'; ++i){
ch = message[i];

if(ch >= 'a' && ch <= 'z'){
ch = ch + key;

if(ch > 'z'){
ch = ch - 'z' + 'a' - 1;
}

message[i] = ch;
}
else if(ch >= 'A' && ch <= 'Z'){
ch = ch + key;

if(ch > 'Z'){
ch = ch - 'Z' + 'A' - 1;
}

message[i] = ch;
}
}

cout << "Encrypted message: " << message;

return 0;
}
Output

Enter a message to encrypt: asd zf
Enter key: 3
Encrypted message: dvg ci

Decryption

#include<iostream>

using namespace std;

int main()
{
char message[100], ch;
int i, key;

cout << "Enter a message to decrypt: ";
cin.getline(message, 100);
cout << "Enter key: ";
cin >> key;

for(i = 0; message[i] != '\0'; ++i){
ch = message[i];

if(ch >= 'a' && ch <= 'z'){
ch = ch - key;

if(ch < 'a'){
ch = ch + 'z' - 'a' + 1;
}

message[i] = ch;
}
else if(ch >= 'A' && ch <= 'Z'){
ch = ch - key;

if(ch > 'a'){
ch = ch + 'Z' - 'A' + 1;
}

message[i] = ch;
}
}

cout << "Decrypted message: " << message;

return 0;
}
Output

Enter a message to decrypt: az GjK
Enter key: 2
Decrypted message: yx EhI

Comment below if you have doubts or found anything incorrect in above program for caesar cipher in C and C++.