Function doesn't return expected value and printf doesn't return any value

Question

Hi I am new to C but not to programming(Only have experience in high-level languages like Python and JS).

In my CS assignment I have to implement a function that decodes an encrypted string.(The encryption used is atbash)

I want to give the decode-function a encoded string and receive a decoded string. I tested my function by printing out every decoded character of the string and it worked.

However I am having issues implementing the original task of the function (encoded str -> decoded str)

Here is my code:

#include <stdio.h>
#include <string.h>

/*******************/
// atbash decoding function
// recieves an atbash string and returns a decoded string.
char *decode(char *str){

  int i = 0;
  char decodedString[1000];
  strcpy(decodedString, "\n");

  while(str[i] != '\0') {

    if(!((str[i] >= 0 && str[i] < 65)||(str[i] > 90 && str[i] < 97)||(str[i] > 122 && str[i] <=127))){

        if(str[i] >= 'A' && str[i] <= 'Z'){
          char upperCaseLetter = 'Z'+'A'-str[i];
          strcat(decodedString, &upperCaseLetter);
        }

        if(str[i] >= 'a' && str[i] <= 'z'){
          char lowerCaseLetter = 'z'+'a'-str[i];
          strcat(decodedString, &lowerCaseLetter);
        }
      }

    if(((str[i] >= 0&& str[i] < 65)||(str[i] > 90 && str[i] < 97)||(str[i] > 122 && str[i] <= 127))){
      char notALetter = str[i];
      strcat(decodedString, &notALetter);
    }
   i++;
  }
  printf("%s\n", decodedString); // Debug: Checking what I would receive as a return, expected "Hello World!", got binaries
  return decodedString;
}

int main(){


  char *message = "Svool Dliow!";

  printf("This is the decode String:\n%s",(decode(message))); //Expected return of "This is the decode String:\nHello World!", received "This is the decode String:\n" instead



  return 0;
}

Issues:

(1)

I receive in the debug comment some binaries, instead of a string ("Hello World!").

(2)

I don't understand why printf("\n%s", (decoded(message))); doesn't print the callback of function decode ._.

Thanks in advance!

Edit:

Issue (2) was solved thanks to paulsm4

Edit2:

Issue (1) was solved thanks to dbush.