getpixel a bitmap with c++

i tried to use bitmap class like this:

#include "windows.h"
#include "gdiplus.h"
#include "stdio.h"
#include "stdafx.h"
#include "iostream"
using namespace Gdiplus;

void main()
{

Bitmap* mybitmap;
mybitmap = gcnew("C:\\Users\\USER\\Documents\\rumah.bmp",false);
int x;
int y;
Color pixelcolor[1000][1000];
for ( x = 0; x < mybitmap->Width; x++ )
{
for ( y = 0; y < mybitmap->Height; y++ )
{
Color pixelcolor[x][y] = mybitmap->GetPixel( x, y );
cout << "Pixel color " << x << ", " << y; "is " << pixelcolor[x][y];
}
}
printf("The width of the image is %u.\n", image->GetWidth());
printf("The height of the image is %u.\n", image->GetHeight());

}</pre>
Error list:

Error 3 error C2871: 'Gdiplus' : a namespace with this name does not exist c:\users\user\documents\visual studio 2008\projects\getpixel\getpixel\getpixel.cpp 6 Error 4 error C2065: 'Bitmap' : undeclared identifier c:\users\user\documents\visual studio 2008\projects\getpixel\getpixel\getpixel.cpp 11

I dont know why Gdiplus namespace doesn't exist... Could you give me some thinking?