Re: class matrix

From:

Larry I Smith <larryXiXsmith@verizon.net>

Newsgroups:

comp.lang.c++

Date:

Sun, 21 May 2006 18:53:54 GMT

Message-ID:

<6H2cg.4757$Ar6.4373@trnddc02>

wojtas.wtk@gmail.com wrote:

This program is compiled, but it is not wanted to start up. Why?

#include <iostream>
using namespace std;

class matrix2x2{

If your compiler complains about access to 'M' (mine does not),
then change the next line to "protected:".

private:
    double M[2][2];
public:
    matrix2x2 (const double tab[][2]);
    matrix2x2(double,double,double,double);
    matrix2x2();
    matrix2x2 operator + (matrix2x2);
    matrix2x2 operator = (matrix2x2);
    matrix2x2 operator - () {
        cout <<"operator -" << endl;
        M[0][0]=-M[0][0];
        M[0][1]=-M[0][1];
        M[1][0]=-M[1][0];
        M[1][1]=-M[1][1];
        return *this;
    }

Use references for 'os' and 'X' in the 'friend' declaration,
like this:

friend ostream& operator << (ostream& os, const matrix2x2& X);

friend ostream& operator << (ostream os, const matrix2x2 X);
double det() {return M[0][0]*M[1][1]-M[1][0]*M[0][1];}
};

Then add the function body for the 'ostream friend' (using
John Carson's code as an example):

ostream& operator<<(ostream& os, const matrix2x2& X)
{
     int i,j;
     for (i=0;i<2;i++)
    {
          for (j=0;j<2;j++)
               cout << X.M[i][j] << ' ';
          cout << '\n';
    }
     return os;
}

matrix2x2::matrix2x2 (const double tab[][2]){
    int i,j;
    for (i=1;i<2;i++)
        for (j=0;j<2;j++)
            M[i][j]=tab[i][j];
}

matrix2x2::matrix2x2(double a, double b, double c, double d) {
    M[0][0]=a;
    M[0][1]=b;
    M[1][0]=c;
    M[1][1]=d;
}

matrix2x2::matrix2x2(){
    M[0][0]=0;
    M[0][1]=0;
    M[1][0]=0;
    M[1][1]=0;
}

matrix2x2 matrix2x2::operator + (matrix2x2 X){
    matrix2x2 T;
    T.M[0][0]=M[0][0] + X.M[0][0];
    T.M[0][1]=M[0][1] + X.M[0][1];
    T.M[1][0]=M[1][0] + X.M[1][0];
    T.M[1][1]=M[1][1] + X.M[1][1];
    return T;
}

matrix2x2 matrix2x2::operator = (matrix2x2 X){
    matrix2x2 T;
    T.M[0][0]=X.M[0][0];
    T.M[0][1]=X.M[0][1];
    T.M[1][0]=X.M[1][0];
    T.M[1][1]=X.M[1][1];
    return T;
}

/*matrix2x2 matrix2x2::operator- (){
    matrix2x2 T;
    T.M[0][0]=-X.M[0][0];
    T.M[0][1]=-X.M[0][1];
    T.M[1][0]=-X.M[1][0];
    T.M[1][1]=-X.M[1][1];
    return T;
}
*/
//int main()
int main(int argc, char **argv)
{
  const double tab[][2]= {{1.5, 2.5}, {3.5, 4.5}};

  matrix2x2 A(tab), B(1.0, 0.0, 0.0, -1.0), C = A + B, D;

  D = -C;

  cout << "\nMacierz A: " << A
       << ", macierz B: " << B
       << ", macierz C: " << C
       << ", macierz D: " << D
       << ", wyznacznik macierzy A: " << A.det() //-2.0
       << ", wyznacznik macierzy B: " << B.det() //-1.0
       << ", wyznacznik macierzy C: " << C.det() // 0.0
       << ", wyznacznik macierzy D: " << D.det(); // 0.0

  return 0;
}

Regards,
Larry