我是vc++菜鸟,写windows程序时，编译生成exe文件运行cpu 占用率100%????

#include "windows.h"
#include "stdio.h"
#include "string.h"

LRESULT CALLBACK WinProc(HWND hWnd,UINT Message,WPARAM wParam,LPARAM lParam);


int WINAPI WinMain(HINSTANCE hInstance,HINSTANCE hPrevInstance,LPSTR lpCmdLine,int nShowCmd)
        {
            HWND hWnd;
            MSG Message;
            WNDCLASS WndClass;
            WndClass.hInstance=hInstance;
            WndClass.lpfnWndProc=WinProc;
            WndClass.lpszClassName="whyan";
            WndClass.lpszMenuName=NULL;
            WndClass.style=0;
            WndClass.cbClsExtra=0;
            WndClass.cbWndExtra=0;
            WndClass.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);
            WndClass.hCursor=LoadCursor(NULL,IDC_ARROW);
            WndClass.hIcon=LoadIcon(NULL,IDI_APPLICATION);
            RegisterClass(&WndClass);

            hWnd=CreateWindow("whyan","whyan",WS_OVERLAPPEDWINDOW,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,NULL,NULL,hInstance,NULL);
            ShowWindow(hWnd,SW_SHOWNORMAL);
            UpdateWindow(hWnd);

            while(GetMessage(&Message,hWnd,0,0))
            {
                TranslateMessage(&Message);
                DispatchMessage(&Message);
            }
            return Message.wParam;
        }

LRESULT CALLBACK WinProc(HWND hWnd,UINT Message,WPARAM wParam,LPARAM lParam)
        {
            HDC hdc;
            HBRUSH hbrush;
            HPEN pen;
            PAINTSTRUCT pstr;
                
            switch (Message)
            {
            case WM_PAINT:
                hdc=BeginPaint(hWnd,&pstr);
                SetMapMode(hdc,MM_ANISOTROPIC);
                pen=(HPEN)GetStockObject(BLACK_PEN);
                hbrush=(HBRUSH)GetStockObject(DKGRAY_BRUSH);
                SelectObject(hdc,hbrush);
                SelectObject(hdc,pen);
                RoundRect(hdc,50,120,100,200,15,15);
                EndPaint(hWnd,&pstr);
            case WM_DESTROY:
                PostQuitMessage(0);
                
            default:
                return(DefWindowProc(hWnd,Message,wParam,lParam));
            }
            //return 0;
        }