mfc 计算器中sin ,log ,和ln函数怎么写

mfc 计算器中sin ,log ,和ln函数怎么写在我的源程序上修改.有意的,我把源程序发过来.void CMy2008110139Dlg::OnBUTTONdaoshu() //求倒数运算{// TODO:Add your control notification handler code hereif(m_val=='0')if(m_val=='0'){m_val="除数不能为零";UpdateData(false);}else{double c;UpdateData();a=atof(m_val);c=1/a;m_val.Format("%f",c);UpdateData(false);}}void CMy2008110139Dlg::OnBUTTONpingfang() //求平方运算{// TODO:Add your control notification handler code heredouble c;UpdateData();a=atof(m_val);c=a*a;m_val.Format("%f",c);UpdateData(false);}void CMy2008110139Dlg::OnBUTTONsin() {// TODO:Add your control notification handler code here这里的代码怎么写?