Let$$s start with Fisher$-$Yates. Write a function $($shuffle$())$ that takes the encryption key $($an array of $26$ char$)$ as a parameter. This function will implement Fisher$-$Yates to change the order of the letters in the key.

We will need to make two arrays of $26$ characters. One for the $$real$$ encryption key and one to hold what the player has entered so far. Since these are fixed in size and small, we don$$t need to use malloc$()$ for them $$ we can make regular old arrays.

Now let$$s take a look at initialization$().$ We will get the puzzle $($like before$),$ but now we will generate the encrypted string. To do this:

$1)$ Generate the ordered encryption key $($use a loop$)$ and call shuffle$()$ on it$.$

$2)$ Populate the player$$s key with $\backslash 0($the NUL character$).$

$3)$ Build the encrypted string:

a$.$ Allocate memory for it$.$

b$.$ Loop over the original string.

i$.$ If the current character is a letter, get the upper case, look it up in the encryption key and append to the encrypted string the encrypted value

ii$.$ Otherwise, output the original $($this preserves spaces, commas, etc$).$

c$.$ NUL terminate the encrypted string

We will change updateState to accept a pair. If the input is not NULL and is not $$quit$,$ then if it is $2$ characters long, we will populate the player$$s key with this new mapping. The first character is the distance, the second is the replacement. If the player entered something else, output a reasonable error message.

We will change displayWorld. It will output the encrypted string and the player$$s progress:

Encrypted: QZZ ZQZ

Decrypted: $\_\_\_\_\_\_$

The rule for decrypted:

if the encrypted character is A$-$Z$,$

look that character up in the player$$s key. If the key is $\backslash 0,$ output $\_,$

otherwise output the key.

Else

Output the encrypted character $($spaces$,$ punctuation, etc.$)$

Finally, in teardown, make sure that you free the memory that you allocated for the encrypted string.

With this work done, we can actually $($sort of$)$ play the game. We can enter pairs and see the decoded string.

Some useful C library functions you might need:

random$()$ time$()$ srandom$()$

strlen$()$ isalpha$()$ toupper$()$

malloc$()$ free$()$

Your program must run through Valgrind without any memory leaks.