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i wanted to practise some basic c++ stuff. I focused on inheritance just to experiment with that. Everything went well until i faced some strange problem: 'cout' was not declared in this scope. I have looked on some topics but on most of them the hints were like append library or write 'using namespace std' but it doesn't solve my problem.

#include <iostream>

class podst
{
public:
    float a;
    float b;
    float dodaw();
    podst(float c,float d) : a(c), b(d)
    {

    }
};
float podst::dodaw()
{
    return (a+b);
}

class poch : public podst
{
    poch() : podst(5,4)
    {
       cout << a << endl << b << dodaw() << endl;
    }

};


using namespace std;
int main()
{
    podst podst(1,2);
    cout <<  podst.dodaw() << endl;
    poch poch2;

    return 0;


}
alaskaman
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  • It's much better to utilize `std::cout` instead of `using namespace std;` at all. https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice – Shady Atef Dec 14 '17 at 21:53

6 Answers6

2

the using namespace std is below the first time you use cout. try using std::cout and std::endl in the poch class.

Audrey Brooke
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  • +1. And, even better, instead of using `std::endl`, use `'\n'`. This code doesn't need the extra stuff that `std::endl` does. – Pete Becker Dec 14 '17 at 22:37
1

poch calls cout from global namespace, not from std namespace. Notice that using namespace std; directive is actually below it, not above. If you don't want to write whole namespace prefix every time it would be better to place that directive on per-function basis, rather then per-file basis:

poch() : podst(5,4)
{
   using namespace std;
   cout << a << endl << b << dodaw() << endl;
}

This approach will help to keep large code bases in piece.

user7860670
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1

If you want to omit the standard library namespace caller ::std, you should write 

using namespace std;

before (usually written right after #include statements and before int main()"

cout << ...

as the compiler reads the code sequentially. Note that it is considered bad practice to use 'using'. I recommend getting used to using with the std:: namespace caller as such:

std::cout << "Hello World!" << std::endl;

To fix your specific problem:

#include <iostream>

using namespace std;

class podst { ...
Arnaud Dhaene
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0

A using declaration starts to take effect at the point where you write it. Since the call to cout is above that point it isn’t covered by the using and you’ll have to spell out std::cout there.

You should avoid using namespace std. A better alternative is to only pull in what you need, e.g. with using std::cout;. But the even better choice is to just use the qualified names. It’s a bit more to type, but it prevents ambiguity; and the qualified names are so ubiquitous in every code base I’ve seen that – at least to me – an unqualified name like cout is always a bit surprising and trips me up slightly when reading code.

besc
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well since poch is a class inheriting from a parent class you needed to either declare the standard namespace at the beginning of the file to make it global to all classes and functions but you declared it before main so the poch class was not able to make use of it, rather you could have explicitly used std::cout and std::endl and the program would have no trouble compiling.

Frank Siwale
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  • I've recommended your other answer to be deleted. If you have more content to add, use the "Edit" button to edit an existing answer and improve on it, rather than create multiple answers to a single question. – Stephen Quan Dec 14 '17 at 23:11
0
class poch : public podst
{
    poch() : podst(5,4)
    {
       //you should have used std::cout
       std::cout << a << endl << b << dodaw() << std::endl;
    }

};
Frank Siwale
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