紧急求救！ 请指教有关声音的问题

小弟想请问有没有什么函数或方法能够控制（增大或减少）播放声音的音量啊？？？
小弟还想请教一个问题：请看以下一段代码
#include "stdafx.h"
#include "PlaySound.h"
#include "PlaySoundDlg.h"
#include "mmsystem.h"
#ifdef _DEBUG
#define new DEBUG_NEW
#undef THIS_FILE
static char THIS_FILE[] = __FILE__;
#endif/////////////////////////////////////////////////////////////////////////////
// CAboutDlg dialog used for App Aboutclass CAboutDlg : public CDialog
{
public:
CAboutDlg();// Dialog Data
//{{AFX_DATA(CAboutDlg)
enum { IDD = IDD_ABOUTBOX };
//}}AFX_DATA // ClassWizard generated virtual function overrides
//{{AFX_VIRTUAL(CAboutDlg)
protected:
virtual void DoDataExchange(CDataExchange* pDX);    // DDX/DDV support
//}}AFX_VIRTUAL// Implementation
protected:
//{{AFX_MSG(CAboutDlg)
//}}AFX_MSG
DECLARE_MESSAGE_MAP()
};CAboutDlg::CAboutDlg() : CDialog(CAboutDlg::IDD)
{
//{{AFX_DATA_INIT(CAboutDlg)
//}}AFX_DATA_INIT
}void CAboutDlg::DoDataExchange(CDataExchange* pDX)
{
CDialog::DoDataExchange(pDX);
//{{AFX_DATA_MAP(CAboutDlg)
//}}AFX_DATA_MAP
}BEGIN_MESSAGE_MAP(CAboutDlg, CDialog)
//{{AFX_MSG_MAP(CAboutDlg)
// No message handlers
//}}AFX_MSG_MAP
END_MESSAGE_MAP()/////////////////////////////////////////////////////////////////////////////
// CPlaySoundDlg dialogCPlaySoundDlg::CPlaySoundDlg(CWnd* pParent /*=NULL*/)
: CDialog(CPlaySoundDlg::IDD, pParent)
{
//{{AFX_DATA_INIT(CPlaySoundDlg)
//}}AFX_DATA_INIT
// Note that LoadIcon does not require a subsequent DestroyIcon in Win32
m_hIcon = AfxGetApp()->LoadIcon(IDR_MAINFRAME);
}void CPlaySoundDlg::DoDataExchange(CDataExchange* pDX)
{
CDialog::DoDataExchange(pDX);
//{{AFX_DATA_MAP(CPlaySoundDlg)
DDX_Control(pDX, IDC_SLIDER1, m_slid);
//}}AFX_DATA_MAP
}BEGIN_MESSAGE_MAP(CPlaySoundDlg, CDialog)
//{{AFX_MSG_MAP(CPlaySoundDlg)
ON_WM_SYSCOMMAND()
ON_WM_PAINT()
ON_WM_QUERYDRAGICON()
ON_BN_CLICKED(IDC_BUTTON1, OnButton1)
ON_MESSAGE(MM_MCINOTIFY,MciNotify)
//}}AFX_MSG_MAP
END_MESSAGE_MAP()/////////////////////////////////////////////////////////////////////////////
// CPlaySoundDlg message handlersBOOL CPlaySoundDlg::OnInitDialog()
{
CDialog::OnInitDialog(); // Add "About..." menu item to system menu. // IDM_ABOUTBOX must be in the system command range.
ASSERT((IDM_ABOUTBOX & 0xFFF0) == IDM_ABOUTBOX);
ASSERT(IDM_ABOUTBOX < 0xF000); CMenu* pSysMenu = GetSystemMenu(FALSE);
if (pSysMenu != NULL)
{
CString strAboutMenu;
strAboutMenu.LoadString(IDS_ABOUTBOX);
if (!strAboutMenu.IsEmpty())
{
pSysMenu->AppendMenu(MF_SEPARATOR);
pSysMenu->AppendMenu(MF_STRING, IDM_ABOUTBOX, strAboutMenu);
}
} // Set the icon for this dialog.  The framework does this automatically
//  when the application's main window is not a dialog
SetIcon(m_hIcon, TRUE); // Set big icon
SetIcon(m_hIcon, FALSE); // Set small icon
// m_slid.SetRange(0,
// TODO: Add extra initialization here
mciopen.dwCallback=0;
mciopen.lpstrAlias=NULL;
mciopen.lpstrDeviceType=TEXT("waveaudio");
mciopen.lpstrElementName=TEXT("C:\\xz.mp3");
mciopen.wDeviceID=0;
mciSendCommand(0,MCI_OPEN,MCI_OPEN_ELEMENT|MCI_WAIT,(DWORD)(LPMCI_OPEN_PARMS)&mciopen);

mcistatus.dwCallback=0;
mcistatus.dwItem=MCI_STATUS_LENGTH ;
mcistatus.dwTrack=MCI_TRACK ;
mciSendCommand(mciopen.wDeviceID,MCI_STATUS,MCI_STATUS_ITEM ,(DWORD)(LPMCI_STATUS_PARMS)&mcistatus);
    int i=mcistatus.dwReturn;
int j=mcistatus.dwItem;
i=i/1000;
j=i%60;
i=i/60;
CString str;
str.Format("%d:0%d",i,j);
SetWindowText(str);
return TRUE;  // return TRUE  unless you set the focus to a control
}void CPlaySoundDlg::OnSysCommand(UINT nID, LPARAM lParam)
{
if ((nID & 0xFFF0) == IDM_ABOUTBOX)
{
CAboutDlg dlgAbout;
dlgAbout.DoModal();
}
else
{
CDialog::OnSysCommand(nID, lParam);
}
}// If you add a minimize button to your dialog, you will need the code below
//  to draw the icon.  For MFC applications using the document/view model,
//  this is automatically done for you by the framework.void CPlaySoundDlg::OnPaint() 
{
if (IsIconic())
{
CPaintDC dc(this); // device context for painting SendMessage(WM_ICONERASEBKGND, (WPARAM) dc.GetSafeHdc(), 0); // Center icon in client rectangle
int cxIcon = GetSystemMetrics(SM_CXICON);
int cyIcon = GetSystemMetrics(SM_CYICON);
CRect rect;
GetClientRect(&rect);
int x = (rect.Width() - cxIcon + 1) / 2;
int y = (rect.Height() - cyIcon + 1) / 2; // Draw the icon
dc.DrawIcon(x, y, m_hIcon);
}
else
{
CDialog::OnPaint();
}
}// The system calls this to obtain the cursor to display while the user drags
//  the minimized window.
HCURSOR CPlaySoundDlg::OnQueryDragIcon()
{
return (HCURSOR) m_hIcon;
}void CPlaySoundDlg::OnButton1() 
{
// TODO: Add your control notification handler code here
    mciset.dwCallback=0;
//mciset.dwAudio=0;
mciset.dwTimeFormat=MCI_FORMAT_BYTES ;
mciSendCommand(mciopen.wDeviceID,MCI_SET,MCI_SET_TIME_FORMAT ,(DWORD)(LPMCI_SET_PARMS)&mciset); MCI_PLAY_PARMS mciplay;
mciplay.dwCallback=(DWORD)this->m_hWnd;
mciplay.dwFrom=10000;
// mciplay.dwTo=90000;
mciSendCommand(mciopen.wDeviceID,MCI_PLAY,MCI_NOTIFY|MCI_FROM,(DWORD)(LPMCI_PLAY_PARMS)&mciplay);
}
void CPlaySoundDlg::MciNotify(WPARAM wparam,LPARAM lparam)
{
if(wparam==MCI_NOTIFY_SUCCESSFUL)
MessageBox("luheng");}
小弟只是想问在onbutton1函数中为什么我的mciplay里的dwto没有起作用，而dwfrom就起了作用。而且我的时间格式是定义了字节，但是却在10秒的时候起动了。不知道是不是我的mciset有问题，有待指教