Caesar Cipher Program

*PROGRAM*

#include<stdio.h>

#include<conio.h>

int main()

{

char message[100], ch;

int i, key,choice;

do

{

printf("\nSelect the options\n");

printf("1. Encryption \t\t 2. Decryption \t\t 3.Exit\n");

scanf("%d",&choice);

switch(choice)

{

case 1:

printf("Enter a message to encrypt: ");

scanf("%s",&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\n", message);

break;

case 2:

printf("Enter a message to decrypt: ");

scanf("%s",&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\n", message);

break;

case 3:

break;

}

}while(choice<3);

return 0;

}

*OUTPUT*