CC65 hello world demo for NES with a fix (wa) for the open gap on the bottom line (taken from https://github.com/cc65/cc65/blob/master/samples/hello.c)

hello.c

#include <stdlib.h>
#include <string.h>
#include <conio.h>
#include <joystick.h>
#include <nes.h>

static const char text[] = "get on that nesdev";

int main(void)
{
    unsigned char xsize, ysize;

    /* Clear the screen, put cursor in upper left corner */
    clrscr();

    (void) textcolor(COLOR_WHITE);
    (void) bordercolor(COLOR_BLACK);
    (void) bgcolor(COLOR_BLACK);

    /* Ask for the screen size */
    screensize(&xsize, &ysize);

    /* Draw a border around the screen */
    // gotoxy(0, 0);

    /* Top line */
    cputc(CH_ULCORNER);
    chline(xsize - 2);
    cputc(CH_URCORNER);

    // /* Vertical line, left side */
    cvline(ysize - 1);

    // /* Bottom line */
    cputc(CH_LLCORNER);
    chline(xsize - 2);
    cputc(CH_LRCORNER);

    // /* Vertical line, right side */
    cvlinexy(xsize - 1, 1, ysize - 1);

    // /* Write the greeting in the mid of the screen */
    gotoxy((xsize - strlen(text)) / 2, ysize / 2);
    cprintf("%s", text);

    // a workaround for the bug where a hline piece is missing in the bottom line
    cputs(" ");

    /* Wait for the user to press a button */
    joy_install (joy_static_stddrv);
    while (!joy_read (JOY_1)) ;
    joy_uninstall ();

    /* Clear the screen again */
    clrscr();

    /* Done */
    return EXIT_SUCCESS;
}

Output: