C++ (Qt)
QWidget * w;
QLineEdit * e = static_cast <QLineEdit *> (w);
if (e)
{
  // OK
}
 

C++ (Qt)
struct Matrix2x2 { 
 double m00, m01, m10, m11;
};
 
void Transform( const Matrix2x2 & m, float * ioX, float * ioY )
{
 double x = *ioX;
 double y = *ioX;
 
 *ioX = x * m.m00 + y * m.m10; 
 *ioY = x * m.m10 + y * m.m11; 
}
 

C++ (Qt)
struct Matrix2x2 { 
 double m00, m01, m10, m11;
};
 
void Transform( const Matrix2x2 & m, float * ioX, float * ioY )
{
 double x = *ioX;
 double y = *ioX;
 
 *ioX = x * m.m00 + y * m.m10; 
 *ioY = x * m.m10 + y * m.m11; 
}
 

C++ (Qt)
struct Matrix2x2 { 
 double m00, m01, m10, m11;
};
 
void Transform( const Matrix2x2 & m, float * ioX, float * ioY )
{
 double x = *ioX;
 double y = *ioX;
  //IMHO: there's no difference in this situation whether I'll write explicit conversion in c++ style or in c-style
  //however i know few about c language, so I'd prefer to do everything in c++ way rather than in c-way
 *ioX = static_cast<float>(x * m.m00 + y * m.m10); //or in C-style (float)(x * m.m00 + y * m.m10) 
 *ioY = static_cast<float>(x * m.m10 + y * m.m11); //or in C-style (float)(x * m.m00 + y * m.m10)
}