Exercice Langage C++ les fonctions amies

#include <iostream.h>
#include <string.h>
class matrice;
class vect{
double x;
double y;
double z;
public:
vect(double a=0,double b=0,double c=0);
void affiche();
friend vect prod(matrice b, vect a);
};
class matrice{
double tableau[3][3];
public :
//friend class a;
matrice(double tab[3][3]=0);
friend vect prod(matrice b, vect a);
};
vect::vect(double a,double b, double c){
x=a;
y=b;
z=c;
}
void vect::affiche(){
cout<<"X= "<<x<<endl;
cout<<"Y= "<<y<<endl;
cout<<"Z= "<<z<<endl;
}
matrice::matrice(double tab[3][3]){
tableau[3][3]=tab[3][3];
tableau[0][0]=1;
tableau[0][1]=2;
tableau[0][2]=3;
tableau[1][0]=4;
tableau[1][1]=5;
tableau[2][1]=6;
tableau[0][2]=7;
tableau[1][2]=8;
tableau[2][2]=9;
}
vect prod(matrice b, vect a){
vect c;
c.x=(b.tableau[0][0]*a.x)+(b.tableau[0][1]*a.y)+(b.tableau[0][2]*a.z);
c.y=(b.tableau[1][0]*a.x)+(b.tableau[1][1]*a.y)+(b.tableau[1][2]*a.z);
c.z=(b.tableau[2][0]*a.x)+(b.tableau[2][1]*a.y)+(b.tableau[2][2]*a.z);
cout<<"le résultat de la multiplication est
:"<<c.x<<","<<c.y<<","<<c.z<<endl;
return c;
}
void main(){
vect vecteur(1,1,1);
matrice mat;
vect res;
res=prod(mat,vecteur);
}