求大神帮忙看一下c++代码哪里错了，谢谢

#include<Windows.h>
#include<tlhelp32.h>
#include<shlwapi.h>
#include<psapi.h>
#include<commctrl.h>
using namespace std;
int main()
{
    HDC a;
    int x=0,y=0;
    a=GetDC(GetDesktopWindow());
    while(true){
        //if(y>=GetSystemMetrics(SM_CYSCREEN)){
        //  x=0;
        //  y=0;
        //}
    StretchBlt(a,x+25,y+25,
    GetSystemMetrics(SM_CXSCREEN)-(x+25)*2,
    GetSystemMetrics(SM_CYSCREEN)-(y+25)*2,
    a, 0, 0,GetSystemMetrics(SM_CXSCREEN),
    GetSystemMetrics(SM_CYSCREEN),13369376);
    Sleep(1000);
    }
    return 0;
 }