Why is it mandatory to use namespace std in new IDEs whereas the programs written in Turbo C++/Borland C++ don't require namespace std?

Question

Why is it mandatory to use namespace std in new compilers whereas the programs written in Turbo C++/Borland C++ don't require namespace std ?

This works in old compilers

#include <iostream.h>

int main () {
   cout << "Hello Programmers";

   return 0;
}

but we have to write the below given program in new compilers instead of the above one, as the above programs don't work in new compilers.

#include <iostream>
using namespace std;

int main () {
   cout << "Hello Programmers";

   return 0;
}

Answer 1

That's because turbo-c++ was released even before any c++ standard was released, and they didn't introduce a std namespace.

It was never updated since then.

Also it isn't mandatory to use the using namespace std; statement, but rather discouraged.

The code should be:

#include <iostream>

int main () {
   std::cout << "Hello Programmers";
}

or

#include <iostream>
int main () {
   using std::cout;    
   cout << "Hello Programmers";
}

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Also IMO questions about turbo-c++ are quite futile this time. It's outdated and not remotely has to do anything with modern c++.
If your professors / teachers force you to use it¹, tell them that they're doing it wrong and don't teach c++ in any way.

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¹⁾_{I know it's common at indian schools, but that's simply bad practice, and doesn't have a sound reasoning.
May be they want you to teach some things from scratch, because turbo-c++ doesn't support containers like std::vector or such.
But I still believe that's the wrong approach, because manual memory management is advanced stuff, and shouldn't be used to confuse beginners.}