Sine Wave Generator Win32/SFML

#include <SFML/Graphics.hpp>
#include <windows.h>
#include <cmath>

int w = 800;
int h = 600;

sf::RenderWindow window;

LRESULT CALLBACK WinProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch(message)
    {
        case WM_DESTROY:
        {
            PostQuitMessage(0);
            break;
        }
        case WM_CLOSE:
        {
            DestroyWindow(hwnd);
            break;
        }
        case WM_PAINT:
        {
            int b, c, nw, nh;
            double i, m, x1, y1, x2, y2, l, a, z;
            sf::Vertex vertices[2];

            RECT ClientRect;
            GetClientRect(hwnd, &ClientRect);
            nw = ClientRect.right - ClientRect.left;
            nh = ClientRect.bottom - ClientRect.top;

            sf::View NewView;
            NewView.setSize(nw, nh);
            NewView.setCenter(nw / 2, nh / 2);
            window.setView(NewView);
            window.clear(sf::Color(255, 255, 255));

            z = 5.0;
            a = (nh / 2) - 20;
            l = nw / z;

            i = l / 360.0;
            m = nh / 2;

            x1 = 0;
            y1 = 0;

            for(b = 0; b < z; b++)
            {
                for(c = 0; c < 360; c++)
                {
                    x2 = x1 + i;
                    y2 = std::sin((x2 / i) * (M_PI / 180.0)) * a;
                    vertices[0] = sf::Vertex(sf::Vector2f(x1, y1 + m), sf::Color(0, 0, 0));
                    vertices[1] = sf::Vertex(sf::Vector2f(x2, y2 + m), sf::Color(0, 0, 0));
                    window.draw(vertices, 2, sf::Lines);
                    x1 = x2;
                    y1 = y2;
                }
            }

            window.display();
            break;
        }
        default:
        {
            return DefWindowProc(hwnd, message, wParam, lParam);
        }
    }

    return 0;
}

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    MSG message;
    WNDCLASS w;
    HWND port, wnd;

    w.style = 0;
    w.lpfnWndProc = &WinProc;
    w.cbClsExtra = 0;
    w.cbWndExtra = 0;
    w.hInstance = hInstance;
    w.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    w.hCursor = LoadCursor(NULL, IDC_ARROW);
    w.hbrBackground = NULL;
    w.lpszMenuName = NULL;
    w.lpszClassName = "Sine Wave";
    if(!RegisterClass(&w))
    {
        return 1;
    }

    wnd = CreateWindow(
        "Sine Wave",
        "Sine Wave Generator (Caelan Stewart)",
        WS_OVERLAPPEDWINDOW,
        50, 50,
        800, 600,
        NULL,
        NULL,
        hInstance,
        NULL
    );

    if(wnd == NULL)
    {
        return 1;
    }

    ShowWindow(wnd, nCmdShow);
    UpdateWindow(wnd);

    window.create(wnd);

    while(GetMessage(&message, NULL, 0, 0) > 0)
    {
        TranslateMessage(&message);
        DispatchMessage(&message);
    }

    return message.wParam;
}