Why doesn't my Caesar Cipher program work according to my code? The code compiles, but does not encipher plaintext

Question

I am curious why this code compiles correctly but only returns the plaintext taken from the user. It does not encipher the plaintext even though the algorithm in the code states so.

#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <ctype.h>

int main(void)
{
    string message=get_string("Enter a message to encrypt: \n");
    int key=get_int("Enter a key to encrypt the message: \n");
    char m[strlen(message)];
    strcpy(m, message);
    for(int i=0; i<strlen(message); i++)
    {
        char letter=m[i];
        if(isalpha(m[i])||isupper(m[i])||islower(m[i]))
        {
            if(letter>='a'&&letter<='z')
            {
                letter=letter+key;
                if(letter>'z')
                {
                    letter=letter-'z'+'a'-1;
                    letter=m[i];
                }
                letter=m[i];
            }
            else if(letter>='A'&&letter<='Z')
            {
                letter=letter+key;
                if(letter>'Z')
                {
                    letter=letter-'Z'+'A'-1;
                    letter=m[i];
                }
                letter=m[i];
            }
        }
        printf("%c", m[i]);
    }
    printf("\n");
    return 0;
}

Answer 1

m is never changed after the plaintext is read into it. I suggest taking a closer look at the order of your assignments.