I am new to C++ Programming , What is the difference between these codes , and Which one I should use?

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I got both the codes from Books from an Online PDF

First -

#include <iostream>
int main()
{
std::cout << "Hello World!";
return 0;
}

Second -

#include <iostream>
using namespace std;
int main()
{
    cout << "Hello world!" ;
    return 0;
}
c++
1 Answers

No difference, using namespace std; simply means everything that is otherwise available via std namespace no loner needs the std:: prefix. In a cpp file its a personal preference. In an h file - don't use using namespace std;, this is because std namespace is huge, and you may be not the only one including that h. For a beginner, or 'academic' code in general it doesn't really matter, but believe me, when you are on the receiving end of someone pulling the entire std namespace in on you in a big project, you aren't gonna like it.

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