## nbrconvertalpha

### Instructions

Write a **program** that prints the corresponding letter in the `n` position of the alphabet, where `n` is each argument received.

For example 1 is a, 2 is b, etc. If `n` is not a valid position of the alphabet or if the argument is not an integer, the **program** should print a space (" ").

It should be implemented a flag `--upper` that prints the result in upper case. 

### Usage

```console 
student@ubuntu:~/student/test$ go build
student@ubuntu:~/student/test$ ./nbrconvertalpha

student@ubuntu:~/student/test$ ./nbrconvertalpha 8 5 12 12 15 | cat -e
hello$
student@ubuntu:~/student/test$ ./nbrconvertalpha 12 5 7 5 14 56 4 1 18 25 | cat -e
legen dary$
student@ubuntu:~/student/test$ ./nbrconvertalpha 32 86 h | cat -e
   $
student@ubuntu:~/student/test$ ./nbrconvertalpha --upper 8 5 25  | cat -e
HEY$
```