Bezier Curves and Bezier Surfaces generation with C/C++ in Code::Blocks

The Bezier blending functions BEZ_k,n(u) are the Bernstein polynomials:  BEZ_k,n(u)=C(n,k)u^k(1-u)^n-k
Where the C(n, k) are binomial coefficients.
Equivalently, we can define Bezier blending functions with the recursion calculation.
BEZ_k,n (u) = (1-u) BEZ_k,n-1(u)+u BEZ_k-1,n-1(u), n>k≥1
With BEZ_k,k = u^k , and BEZ_0,k = (1-u)^k.

C Source Code

#include <windows.h>
#include <math.h>
#define ROUND(a) ((int) (a + 0.5)) 
/* set window handle */
static HWND sHwnd;
int a; 
void SetWindowHandle(HWND hwnd){
    sHwnd=hwnd;
} 
void setPixel(int x,int y,COLORREF color){
    if(sHwnd==NULL){
        MessageBox(NULL,"sHwnd was not initialized !","Error",MB_OK|MB_ICONERROR);
        exit(0);
    }
    HDC hdc=GetDC(sHwnd);
    SetPixel(hdc,x,y,color);
    ReleaseDC(sHwnd,hdc);
    return; 
// NEVERREACH // 
} 
float Coeff (int k, int n)
{
    int j;
    float coeff= 1.0;
    for (j=n; j>k; j--)            coeff *= j;
    for (j=n-k; j>k; j--)          coeff /= j;
    return(coeff);
} 
float BValue (int k, int n, float u, float coeff)
{
    int j;
    float bvl = coeff;
    for (j=1; j<=k; j++)           bvl *=u;
    for (j=1; j<=n-k; j++)      bvl *= (1-u);
    return (bvl);
} 
void BezierCurve (int Points, int col,...)
{
    va_list Cord;
    int xpt[10], ypt[10], i=0, j, CP;
    float x,y,u,b,c;
    va_start (Cord,col);
    while (((xpt[i]=(va_arg (Cord,int))) >= -1) &&
    ((ypt[i]=(va_arg (Cord,int))) >= -1)
    && ( i<=20))
    i++;
    va_end (Cord);
    CP = (i-1); 
    for (i=0; i<=Points; i++)
    {
        u = (float)i/Points;
        x = 0;
        y = 0;
        for (j=0; j<=CP; j++)
        {
            c  = Coeff(j,CP);
            b  = BValue (j,CP,u,c);
           x += xpt[j]*b;
           y += ypt[j]*b;
        }
        setPixel(ceil(0.5+x),y,col);
    }
} 
/* Window Procedure WndProc */
LRESULT CALLBACK WndProc(HWND hwnd,UINT message,WPARAM wParam,LPARAM lParam){
    switch(message){
        case WM_PAINT:
            SetWindowHandle(hwnd);
            for(a=0;a<=50;a+=1)
            {
                BezierCurve(2000,RGB(a+100,a,50+a),50,200+a,100+a+a,300+a,150,200+a,200,200+a,-1000);
                BezierCurve(2000,RGB(a+100,a,50+a),200,200+a,300+a+a,300+a,400,200+a,500,200+a,-1000);
                BezierCurve(2000,RGB(a+100,a,50+a),500,200+a,550+a+a,300+a,600,200+a,650,200+a,-1000);
            }
            break;
        case WM_CLOSE: // FAIL THROUGH to call DefWindowProc
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
        default:
        break; // FAIL to call DefWindowProc //
    }
    return DefWindowProc(hwnd,message,wParam,lParam);
} 
int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int iCmdShow){
    static TCHAR szAppName[] = TEXT("Curves");
    WNDCLASS wndclass;
    wndclass.style         = CS_HREDRAW|CS_VREDRAW ;
    wndclass.lpfnWndProc   = WndProc ;
    wndclass.cbClsExtra    = 0 ;
    wndclass.cbWndExtra    = 0 ;
    wndclass.hInstance     = hInstance ;
    wndclass.hIcon         = LoadIcon (NULL, IDI_APPLICATION) ;
    wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;
    wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;
    wndclass.lpszMenuName  = NULL ;
    wndclass.lpszClassName = szAppName ;
    // Register the window //
    if(!RegisterClass(&wndclass)){
        MessageBox(NULL,"Registering the class failled","Error",MB_OK|MB_ICONERROR);
        exit(0);
    } 
    // Createw indow //
    HWND hwnd=CreateWindow(szAppName,"Bezier Curve - Programming Techniques",
                WS_OVERLAPPEDWINDOW,
                 CW_USEDEFAULT,
                 CW_USEDEFAULT,
                 CW_USEDEFAULT,
                 CW_USEDEFAULT,
                 NULL,
                 NULL,
                 hInstance,
                 NULL);
    if(!hwnd){
        MessageBox(NULL,"Window Creation Failed!","Error",MB_OK);
        exit(0);
    } 
    // ShowWindow and UpdateWindow //
    ShowWindow(hwnd,iCmdShow);
    UpdateWindow(hwnd);
    // Message Loop //
    MSG msg;
    while(GetMessage(&msg,NULL,0,0)){
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    /* return no error to the operating system */
    return 0;
}