cerr is undefined

Question

I have some problems, I'm getting these errors (marked in the code):

• identifier "cerr" is undefined
• no operator "<<" matches these operands

Why?

#include "basic.h"
#include <fstream>

using namespace std;

int main()
{

    ofstream output("output.txt",ios::out);
    if (output == NULL)
    {
        cerr << "File cannot be opened" << endl;   // first error here
        return 1;
    }

    output << "Opening of basic account with a 100 Pound deposit: "
        << endl;
    Basic myBasic (100);
    output << myBasic << endl;   // second error here
}

Answer 1

You must include iostream in order to use cerr.
See http://en.cppreference.com/w/cpp/io/basic_ostream.