problems with matrix mult. method

[Captain Penguin]

Hey all, I'm working on a simple 3d engine (probably just a starfield simulation) but am running accross problems in my operator* code (this is for 4x4 matrices):

 M4x4 M4x4::operator*(const M4x4 &mat)
  {
    M4x4 product;
    
    for(int i = 0; i < 4; i++)
      for(int j =0; j < 4; j++)
        product.setValue(i,j, (float)(this->matrix[i][1] * mat.getValue(1,j)
        + this->matrix[i][2] * mat.getValue(2,j)
        + this->matrix[i][3] * mat.getValue(3,j)));
    return product;
  }

where setValue set's matrix[i][j] to a float value and getValue returns the float, matrix[i][j].

I'm getting the following errors in Metrowerks Codewarrior IDE 4.1:

Error   : cannot pass const/volatile data object to non-const/volatile member function
M4x4.cpp line 26   product.setValue(i,j, (float)(this->matrix[i][1] * mat.getValue(1,j)

Error   : cannot pass const/volatile data object to non-const/volatile member function
M4x4.cpp line 27   + this->matrix[i][2] * mat.getValue(2,j)

Error   : cannot pass const/volatile data object to non-const/volatile member function
M4x4.cpp line 28   + this->matrix[i][3] * mat.getValue(3,j)));

Error   : cannot pass const/volatile data object to non-const/volatile member function
M4x4.cpp line 38   sum.setValue(i,j, matrix[i][j] + mat.getValue(i,j));

Which doesn't make a whole lot of sense to me.

is there something wrong with this code? Maybe it's something elsewhere in my code causing this particular section to mess up?

Help please.

[Magos]

product.setValue(i,j, (float)(this->matrix[i][1] * mat.getValue(1,j)

Here (line 26) you're passing a constant variable to a function which take a non-constant variables as an argument. This is invalid, since a function with non-constant arguments are allowed to modify those, but you're passing something that isn't allowed to be modified.