How to simulate mouse moving

I want to simulate mouse moving,but I find it moves litter
and sometimes the display turns black screen,and after
a while the display recovers,why?how to solver?
Look:

Code:

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void CCopyscrnDlg::OnButton1()
{
INPUT mouseInput;
mouseInput.type = INPUT_MOUSE;
mouseInput.mi.dx = 0;
mouseInput.mi.dy = -1;
mouseInput.mi.dwFlags = MOUSEEVENTF_MOVE ; 
SendInput(1, &mouseInput, sizeof(INPUT));
}
void CCopyscrnDlg::OnButton2()
{
INPUT mouseInput;
mouseInput.type = INPUT_MOUSE;
mouseInput.mi.dx = -1;
mouseInput.mi.dy = 0;
mouseInput.mi.dwFlags = MOUSEEVENTF_MOVE ;
SendInput(1,&mouseInput, sizeof(INPUT));
}
void CCopyscrnDlg::OnButton3()
{
INPUT mouseInput;
mouseInput.type = INPUT_MOUSE;
mouseInput.mi.dx = 1;
mouseInput.mi.dy = 0;
mouseInput.mi.dwFlags = MOUSEEVENTF_MOVE ; 
SendInput(1, &mouseInput, sizeof(INPUT));
}
void CCopyscrnDlg::OnButton4()
{
INPUT mouseInput;
mouseInput.type = INPUT_MOUSE;
mouseInput.mi.dx = 0;
mouseInput.mi.dy = 1;
mouseInput.mi.dwFlags = MOUSEEVENTF_MOVE ;
SendInput(1,&mouseInput, sizeof(INPUT));
}

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