SDL hello-world program on ArkOS runs without error, but shows no output

I got it working! The answer was a modification of @Noel Whitemore's loop and putting the SDL_RenderPresent() call inside the loop. The following code now works for drawing and animation.

#include <SDL2/SDL.h>
#include <stdio.h>

#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480

int main(int argc, char* argv[])
{
    // Initialize SDL
    if (SDL_Init(SDL_INIT_EVERYTHING) != 0) {
        printf("SDLInit Error: %s\n", SDL_GetError());
        return 1;
    }

    // Create a window
    SDL_Window *win = SDL_CreateWindow("Hello, World!",
                                       SDL_WINDOWPOS_UNDEFINED,
                                       SDL_WINDOWPOS_UNDEFINED,
                                       SCREEN_WIDTH, SCREEN_HEIGHT,
                                       SDL_WINDOW_FOREIGN);

    if (win == NULL) {
        printf("SDL_CreateWindow Error: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }

    // Create a renderer
    //SDL_Renderer *ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
    SDL_Renderer *ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_SOFTWARE);

    // Setup t0 time using SDL
    Uint32 t0 = SDL_GetTicks();

    if (ren == NULL) {
        SDL_DestroyWindow(win);
        printf("SDL_CreateRenderer Error: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }

    // Event loop
    SDL_bool quit = SDL_FALSE;
    SDL_Event e = { 0 };
    while (!quit) {

        // Poll for events with timeout of 100ms
        e = SDL_Event { 0 };
        SDL_WaitEventTimeout(&e, 10);

        switch (e.type) {
            case SDL_QUIT:
                quit = SDL_TRUE;
                break;
            default:
                break;
        }

        // Set draw the interface
        SDL_SetRenderDrawColor(ren, 0, 0, 255, 255);
        SDL_RenderClear(ren);

        int elapsed = SDL_GetTicks() - t0;
        if ((elapsed / 1000) % 2)
            SDL_SetRenderDrawColor(ren, 0x00, 0xFF, 0x00, 0xFF); // Green
        else
            SDL_SetRenderDrawColor(ren, 0xFF, 0x00, 0x00, 0xFF); // Red

        // Draw and animate
        SDL_Rect fillRect = { SCREEN_WIDTH  / 4 + elapsed / 100, SCREEN_HEIGHT / 4,
                              SCREEN_WIDTH/2, SCREEN_HEIGHT / 2 };
        SDL_RenderFillRect(ren, &fillRect);

        SDL_RenderPresent(ren);

        // Exit after 5 seconds
        if (elapsed > 10000)
            break;
    }    

    // Clean up
    SDL_DestroyRenderer(ren);
    SDL_DestroyWindow(win);
    SDL_Quit();
    printf("ok!\n");

    return 0;
}

```

To fix this issue, it appears that SDL_PollEvent() may need to be called in order to make the window appear and this behaviour can be dependent on the operating system used to run the program. Adding a simple while() loop to keep the program running does not appear to be sufficient to keep a window open. This issue is discussed here: Why does my window only get shown after I use SDL_PollEvent()?

The revised code is as follows:

#include <SDL2/SDL.h>
#include <stdio.h>

int main(int argc, char* argv[]) {
    // Variables used by the event loop
    SDL_bool quit = SDL_FALSE;
    SDL_Event e = { 0 };

    // Initialize SDL
    if (SDL_Init(SDL_INIT_EVERYTHING) != 0) {
        printf("SDL_Init Error: %s\n", SDL_GetError());
        return 1;
    }

    // Create a window
    SDL_Window *win = SDL_CreateWindow("Hello, SDL2!", 100, 100, 640, 480, SDL_WINDOW_SHOWN);
    if (win == NULL) {
        printf("SDL_CreateWindow Error: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }

    // Create a renderer
    SDL_Renderer *ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
    if (ren == NULL) {
        SDL_DestroyWindow(win);
        printf("SDL_CreateRenderer Error: %s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }

    // Set the draw color to blue
    SDL_SetRenderDrawColor(ren, 0, 0, 255, 255);

    // Clear the window
    SDL_RenderClear(ren);

    // Present the window
    SDL_RenderPresent(ren);

    // Event loop
    while (!quit) {
        while (SDL_PollEvent(&e)) {
            switch (e.type) {
                case SDL_QUIT:
                    quit = SDL_TRUE;
                    break;
                default:break;
            }
        }
    }

    // Clean up
    SDL_DestroyRenderer(ren);
    SDL_DestroyWindow(win);
    SDL_Quit();

    return 0;
}