c++ debug '<<' no operator found - c++

Question

I am trying to run the following code on c++ but keep geting error. Can anyone solve it for me please.
the error message from c++ says:
Error 6 error C2679: binary '<<' : no operator found which takes a
right-hand operand of type 'MVector'
#include <iostream>
#include <cmath>
#ifndef MVECTOR_H // the 'include guard'
#define MVECTOR_H // see C++ Primer Sec. 2.9.2
#include <vector>
#include <string>
#include <fstream>
class MVector
{
public:
// constructors
MVector() {}
explicit MVector(int n) : v(n) {}
MVector(int n, double x) : v(n, x) {}
void push_back(double x)
{
v.push_back(x);
}
double AV()
{
double sum = 0.0, average = 0.0;
for (double i = 0; i<v.size(); i++)
{
sum += v[i];
}
average = sum / v.size();
return average;
}
MVector RunningAverage(int m, int p)
{
MVector movingaverage(v.size() - m - p - 1);
for (int i = m; i < v.size() - p; i++)
{
double sum = 0.0;
if ((i + p < v.size()))
{
for (int j = i - m; j <= i + p; j++)
{
sum += v[j];
movingaverage[i - m] = sum / (m + p + 1);
}
}
}
return movingaverage; // Edit by jpo38
}
// access element (lvalue)
double &operator[](int index) { return v[index]; }
// access element (rvalue)
double operator[](int index) const { return v[index]; }
int size() const { return v.size(); } // number of elements
private:
std::vector<double> v;
};
#endif
int main()
{
using namespace std;
// create an MVector
MVector x;
// add elements to the vector
x.push_back(1.3);
x.push_back(3.5);
x.push_back(3.0);
x.push_back(2.0);
// x now contains 1.3 and 3.5
// print x
std::cout << " x:= ( ";
for (int i = 0; i < x.size(); i++)
std::cout << x[i] << " ";
std::cout << ")\n";
std::cout << x.RunningAverage(0, 1.0) << endl;
return 0;
}

Answer 1

x.RunningAverage(0, 1.0) returns a MVector that cannot be sent to std::cout, unless you declare the operator<< taking a MVector as parameter.
Alternatively, you can replace:
std::cout << x.RunningAverage(0, 1.0) << endl;
By:
MVector av = x.RunningAverage(0, 1.0);
for (int i = 0; i < av.size(); i++)
std::cout << av[i] << " ";
Or, declare the operator:
std::ostream& operator<<(std::ostream& out,const MVector& b)
{
for (int i = 0; i < b.size(); i++)
out << b[i] << " ";
return out;
}
And then std::cout << x.RunningAverage(0, 1.0) << std::endl; will work.
And you can then also replace, in your main function:
for (int i = 0; i < x.size(); i++)
std::cout << x[i] << " ";
By:
std::cout << x;
Live demo: http://cpp.sh/7afyi

Answer 2

You haven't overloaded operator<< for MVector.
You can do that with:
std::ostream& operator<<(std::ostream& output, MVector const& vec)
{
// use "output << …;" to do printing
return output;
}