Draw a triangle on Windows using OpenGL 1.1

triangle.c

// Draw a triangle on Windows using OpenGL 1.1
// $ gcc -mwindows -o triangle triangle.c -lopengl32
// This is free and unencumbered software released into the public domain.
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <GL/gl.h>

#define countof(a) (int)(sizeof(a) / (sizeof(*(a))))

static LRESULT CALLBACK handler(HWND h, UINT msg, WPARAM wparam, LPARAM lparam)
{
    switch (msg) {
    case WM_CLOSE:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProcA(h, msg, wparam, lparam);
}

int WINAPI WinMain(HINSTANCE h, HINSTANCE p, LPSTR cmd, int show)
{
    WNDCLASSA wc     = {0};
    wc.lpfnWndProc   = handler;
    wc.lpszClassName = "gl";
    RegisterClassA(&wc);

    DWORD style = WS_MINIMIZEBOX | WS_SYSMENU;
    HWND wnd = CreateWindowA(
        "gl", "Demo", style,
        CW_USEDEFAULT, CW_USEDEFAULT, 800, 600,
        0, 0, 0, 0
    );

    PIXELFORMATDESCRIPTOR pfd = {0};
    pfd.nSize    = sizeof(pfd);
    pfd.nVersion = 1;
    pfd.dwFlags  = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
    HDC dc       = GetDC(wnd);
    int format   = ChoosePixelFormat(dc, &pfd);
    SetPixelFormat(dc, format, &pfd);
    HGLRC ctx    = wglCreateContext(dc);
    wglMakeCurrent(dc, ctx);
    ShowWindow(wnd, SW_NORMAL);

    for (;;) {
        for (MSG msg; PeekMessageA(&msg, 0, 0, 0, TRUE);) {
            if (msg.message == WM_QUIT) {
                ExitProcess(0);
            }
            TranslateMessage(&msg);
            DispatchMessageA(&msg);
        }

        glClearColor(0, 0, 0, 0);
        glClear(GL_COLOR_BUFFER_BIT);

        float triangle[] = {-0.5f,-0.5f, 0.0f,0.5f, 0.5f,-0.5f};
        glVertexPointer(2, GL_FLOAT, 0, triangle);
        glColor3f(1, 0, 1);
        glEnableClientState(GL_VERTEX_ARRAY);
        glDrawArrays(GL_TRIANGLES, 0, countof(triangle)/2);

        SwapBuffers(dc);
    }
}