drawing pixels with SDL

sdl2_pixels.c

// on Windows compile with:
// cl.exe sdl2_pixels.c -Zi -Iinclude -link -incremental:no -subsystem:windows SDL2.lib SDL2main.lib shell32.lib

#include <SDL.h>
#include <math.h>

int main(int argc, char* argv[])
{
    int width = 1280;
    int height = 720;

    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window* window = SDL_CreateWindow("SDL pixels", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, width, height, SDL_WINDOW_SHOWN);
    SDL_Surface* screen = SDL_GetWindowSurface(window);
    SDL_Surface* pixels = SDL_CreateRGBSurfaceWithFormat(0, width, height,32, SDL_PIXELFORMAT_RGBX8888);

    unsigned int t1 = SDL_GetTicks();

    float pos = 0;

    for (;;)
    {
        SDL_Event ev;
        while (SDL_PollEvent(&ev))
        {
            if (ev.type == SDL_QUIT)
            {
                return 0;
            }
        }

        unsigned int t2 = SDL_GetTicks();
        float delta = (t2 - t1) / 1000.0f;
        t1 = t2;

        // clear pixels to black background
        SDL_FillRect(pixels, NULL, 0);

        // write the pixels
        SDL_LockSurface(pixels);
        {
            int pitch = pixels->pitch;

            // move 100 pixels/second
            pos += delta * 100.0f;
            pos = fmodf(pos, width);

            // draw red diagonal line
            for (int i=0; i<height; i++)
            {
                int y = i;
                int x = ((int)pos + i) % width;

                unsigned int* row = (unsigned int*)((char*)pixels->pixels + pitch * y);
                row[x] = 0xff0000ff; // 0xAABBGGRR
            }
        }
        SDL_UnlockSurface(pixels);

        // copy to window
        SDL_BlitSurface(pixels, NULL, screen, NULL);
        SDL_UpdateWindowSurface(window);
    }
}

sdl2_pixels_r.c

// on Windows compile with:
// cl.exe sdl2_pixels_r.c -Zi -Iinclude -link -incremental:no -subsystem:windows SDL2.lib SDL2main.lib shell32.lib

#include <SDL.h>
#include <math.h>

int main(int argc, char* argv[])
{
    int width = 1280;
    int height = 720;

    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window* window = SDL_CreateWindow("SDL pixels", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, width, height, SDL_WINDOW_SHOWN);
    SDL_Renderer* renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
    SDL_Texture* pixels = SDL_CreateTexture(renderer, SDL_PIXELFORMAT_RGBX8888, SDL_TEXTUREACCESS_STREAMING, width, height);

    unsigned int t1 = SDL_GetTicks();

    float pos = 0;

    for (;;)
    {
        SDL_Event ev;
        while (SDL_PollEvent(&ev))
        {
            if (ev.type == SDL_QUIT)
            {
                return 0;
            }
        }

        unsigned int t2 = SDL_GetTicks();
        float delta = (t2 - t1) / 1000.0f;
        t1 = t2;

        void* data;
        int pitch;
        SDL_LockTexture(pixels, NULL, &data, &pitch);
        {
            // clear to black background
            SDL_memset(data, 0, pitch * height);

            // move 100 pixels/second
            pos += delta * 100.0f;
            pos = fmodf(pos, width);

            // draw red diagonal line
            for (int i=0; i<height; i++)
            {
                int y = i;
                int x = ((int)pos + i) % width;

                unsigned int* row = (unsigned int*)((char*)data + pitch * y);
                row[x] = 0xff0000ff; // 0xAABBGGRR
            }
        }
        SDL_UnlockTexture(pixels);

        // copy to window
        SDL_RenderCopy(renderer, pixels, NULL, NULL);
        SDL_RenderPresent(renderer);
    }
}

Hello I found problem.
You should to remove {} after:
SDL_LockTexture(pixels, NULL, &data, &pitch);
It works fine. :)
Result:

Nice idea - I am working on C# :)

Curly braces like that are perfectly valid to use in C code. There's no reason to remove them. They just letting reader of source code to know that these lines of code should "go together" - because texture locking is happening around it.