In Chapter 8 we learned about a simple encryption algorithm

In Chapter 8, we learned about a simple encryption algorithm called a Caesar cipher. Write a program in the language of your choice to implement the Caesar cipher algorithm. Write a main function (method, procedure) that collects a message from the user and writes it out again. Assume for simplicity that the message contains no more than 10 characters and that only the 26 uppercase letters of the alphabet are used. Use an array of 10 elements to store the message. Ask the user to enter no more than 10 characters, one per line, and to terminate the message by entering some special character such as \"%.\" Use a variable to keep track of the number of array elements actually used (which could be fewer than 10 if the message is short) so that you do not write out meaningless characters stored at the end of the array.

Solution

Solution:

Please find the explanation in the comments for the encryption:

Note: Use of shorthand notation for small operations helps in code-optimization and is also a decent programming practice.

CeaserCipher.java

import java.util.Scanner;

public class CeaserCipher {

public static void main(String[] args) {
int counter = 0, shift = 0;
Scanner reader = new Scanner(System.in);

System.out.println(\"Enter the characters [Max length is 10, use \\\"%\\\" for deliminating your input before entering 10 characters]:\");
char[] inputArray = new char[10];
while(counter < 10){
inputArray[counter] = reader.next().trim().charAt(0);
if(inputArray[counter] == \'%\'){
//omitting the terminator character with the default value of a char[]
inputArray[counter] = \'\\u0000\';
break;
}
counter++;
}
System.out.println(\"Enter the shift:\");
shift = reader.nextInt();

System.out.println(\"***********\");
System.out.println(\"Befor encryption:\");
for(int i = 0; i< counter; i++){
System.out.print(inputArray[i]+\" \");
}
System.out.println();

  
//Logic for encryption : shifting the character by the designated
//shift
for(int i = 0; i< counter ; i++){
//Taking the present character as buffer
char buffer = inputArray[i];

//Shifting the buffer with specified shift
buffer+=shift;

//Checking whether the buffer is in the permissible ASCII value
//range for upper case characters or not
if(buffer > 90){   
int offSet = buffer - 90;
offSet+=65;
inputArray[i] = (char)offSet;
}else{
inputArray[i] = buffer;
}
}

System.out.println(\"***********\");
System.out.println(\"After encryption:\");
for(int i = 0; i< counter; i++){
System.out.print(inputArray[i]+\" \");
}
System.out.println();
System.out.println(\"***********\");

}
}