#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void PrinterFunction(void)
{
    // both the alphabet and its size are constants. the size is reduced by
    //  one to account for the terminating nullchar, which we do *NOT* want
    //  as a viable choice of letters.
    static const char alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    static const size_t alpha_size = sizeof alphabet/sizeof *alphabet - 1;

    // open the file
    FILE *fp = fopen("Default.txt", "a");
    if (fp == NULL)
    {
        perror("Defaults.txt : ");
        exit(EXIT_FAILURE);
    }

    // generate a two-character random selection from the alphabet characters
    char str[3] =
    {
        alphabet[rand() % alpha_size],
        alphabet[rand() % alpha_size],
        0
    };

    // write to output, followed by newline
    fputs(str, fp);
    fputc('\n', fp);

    // close the file.
    fclose(fp);
}