operators in class vectors

[Lane]

Hi guys, if i have a class declaration that looks like

class Vector 
{
    int ndim;
    double* data;
    
public:
     Vector( int n, double d[]);
    ~Vector();
//some functions here
  
    friend double operator*(const Vector& p,const Vector& q);
    friend ostream& operator<<(ostream& s, Vector& p);

can i initialise

    friend double operator*(const Vector& p,const Vector& q);
    friend ostream& operator<<(ostream& s, Vector& p);

This way?

double operator*(const Vector& p,const Vector& q)
{
     double c = 0;
     for (int i=0; i<4; i++)
     c+= p.data[i]*q.data[i];
     return c;
     }

ostream& operator<<(ostream& s, Vector& p){
     return s <<"("<<p.data[0]<<" , "<<p.data[1]<<" , "<<p.[2]<<" , "<<p.[3]<<")";
     }

[hamsterman]

both ignore ndim and expect it to be 4. in operator *, you just have to replace 4 with ndim on line 4. in operator <<, you have to have a for loop. also, p.[2] DOES NOT MAKE SENSE!

don't start multiple threads about the same problem.

[Lane]

Thanks hamsterman. but if i make the operator* to be

double operator*(const Vector& p,const Vector& q)
{
     int ndim;
     double c = 0.0;
     for (int i=0; i<ndim; i++)
     c+= p.data[i]*q.data[i];
     return c;
     }

and

ostream& operator<<(ostream& s, Vector& p){
     
     for (int k = 0; k  < p.ndim; k++)
     s << p.data[k];
     return s;
     }

in the main

int main()
{
      int n;
      double* data = new double[n];
      double a[4]= {1.0, 2.0, 3.0, 4.0};
      double b[4]= {4.0, -5.0, 6.0, -7.0};
    
      Vector c(4, a );
      Vector d(4, b );
      Vector e(c+d);
      double f(d*d);
    
      cout<<e<<endl;
      cout<<f<<endl;

The compiler does not respond.

[Lane]

Thanks hamsterman. I have now cracked it. cool !!