Problem 2:

The Caesar cipher is one of the earliest known and simplest ciphers. It is a type of substitution cipher in

which each letter in the plaintext is 'shifted' a certain number of places (to the left or right) down the

alphabet. This directional substitution over a certain number of places is known as the key of the

substitution cipher. For example, with a right-shift of 1, the alphabet A would be replaced by B, B would

become C, and so on. The method is named after Julius Caesar, who apparently used it to communicate

with his generals.

A full example of the Caesar Cipher using a right-shift-1 key would be as follows:

plaintext: defend east wall of the castle

ciphertext: efgfoe uif fbtu xbmm pg uif dbtumf

Without the knowledge of the key, it will be challenging to easily decipher the actual plain text message.

You have been given an input file called myPlainText.txt (see attachment), which consists of a plaintext

message. Write a C++ code that will read the plaintext message from the input file, convert all the upper

case alphabets to lower case and implement the Caesar substitution cipher using the key: left-shift-4. The

generated cipher text should be written to an output file called myCipherText.txt.

Your submission pdf file should contain your C++ source code, compilation, and the cat (linux

command to paste the contents of a file on the terminal) of your output file.

Note: Your code should work for any cipher key with minimalistic changes. The structure of the input

file must be preserved in the output file (The number of lines and words in each line).

(7 points)

HINTS:

1. To convert upper-case alphabet to its lower-case counter-part you can use the in-built function

tolower(variable);

if you have the following variable:

char variable = C;

And you use tolower() as follows:

cout

it will output the value c.

2. Alphabets are associated with numerical values known as ASCII values. The function prototype

of tolower() is as follows:

int tolower(int variable);

As such in point 1 above, If we didnt cast the cout statement using the datatype char the output

would have been the ASCII of lower-case c which is 99. The complete chart of ASCII values

for the alphabets (A,,Z and a,,z) can be found on https://ascii.cl/ . Use this concept when you

design the logic of your program.

3. For a input line as given below:

Hello my name is

If you want to read the entire line in one go including the white spaces (instead of reading word

by word ignoring the whitespaces) then you can use the function getline() which is used as

follows:

#include

//.

int main()

{

string inputString;

ifstream fin;

// open file and validate etc.

while (!fin.eof())

{

getline(fin, inputString);

}

}

The file input stream object will read an entire line into your string variable. You can then

traverse the string character by character by using the following pseudo code:

char c;

for(unsigned int i = 0; i

{

c = inputString[i]; //this is your character

}

4. If you want to open a write file append mode, use following:

fout.open(output.txt, ios::app);

This is the text file we were given called myPlainText.txt and I am completely lost on using a file as an input and returning an output within a file, please help.

While I pondered weak and weary Over many a quaint and curious volume of forgotten lore While I n dded nearly napping Suddenly there came a tapping As of some ne gently rapping Rapping at mY chamber door Tis some visitEr I muttered tapping aT my chamber door Only this aNd nothing more