C - when I use the site. h scanf does not work well

Question

I’m creating a database.

I used the locale.h and setlocale(LC_ALL, "Portuguese") for accents and cediles to appear on the windows command line.

Because of this when I make one scanf of an accentuated or ceded character and I do the respective printf it prints a nonexistent symbol in the alphabet and the corresponding value in decimal is a negative number.

If the special character is not entered by scanf (or fgets) and you already have the program 'prints it' in the code

I’ve done some research on the subject and found a lot of information about the various types of coding and Unicode but nothing about why this happened.

I leave my code:

# include <stdio.h>
# include <locale.h>

int main() {

    setlocale(LC_ALL, "Portuguese") ;

    /* Para ver a tabela ASCII */

    int x ;

    for(x = 0; x <= 255; x++) {

        printf("[%d]: %c\n", x, x);
    }

    char ch ;

    printf("Introduzir caractere: ")
    scanf("%c", &ch) ;
    printf("Caractere introduzido: %c\n", ch);
    printf("Valor na tabela ASCII: %d\n", ch);
}

by entering, for example, a "ç" the character you print is " " and the decimal value is -121. The same applies to other accented characters.

Why is this happening?