仪表问题

请问要实现点击按钮一次thetaInDegrees+1，应该怎么实现？
void CSpeedmeterDlg::OnPaint() 
{
CPaintDC dc(this); CPen *pOldPen;
CPen *pNewPen=new CPen();
CRect rect;pNewPen->CreatePen(PS_DASH,4,RGB(0,255,0));
pOldPen=dc.SelectObject(pNewPen);
//int thetaInDegrees=m_edit;
int thetaInDegrees=1;
double theta =thetaInDegrees  * (3.14159/180);
int x,y,x1,y1,i,speed;
GetClientRect(&rect);
//speed=3;
x=30;
y=312;
//for(speed>0;x=30;y=312)
//for(i=0;i<speed;i++)
//for(int x = x1; x<=x2; x++)
//  for(int y = x1; y<=y2; y++)
//{
x1=int(x-140)*cos(theta)-(y-312)*sin(theta)+140;
y1=int(x-140)*sin(theta)-(y-312)*cos(theta)+312;
dc.MoveTo(140,312);
dc.LineTo(x1,y1);
//x=x1;
//y=y1;
//}
dc.SelectObject(pOldPen);
pNewPen->DeleteObject();
delete pNewPen;
}