What is the mean of ' using namespace std ; ' ?

Question

please give me that answer

Answer 1

it is for importing the std namespace into your code. if you don't include that line of code, you will have to prefix cout like std::cout, cin becomes std::cin, endl becomes std::endl. Therefore, it makes your lines of code shorter when you write using namespace std.

pls note: std isn't the only namespace you can use in your code. you can create your own namespace and use in your codes. read chapter on namespaces

Answer 2

may you give a example of code ?

Answer 3

Is my code run if I don't write std::cout or std::cin ?
can I use direct cin or cout without write std::cout or std::cin ?

Answer 4

namespace is created to be used as additional information to differentiate functions, classes, variables with the same name available in different libraries. we can say, a namespace tells us the scope of our code

an example is
namespace namespace_name {
// code declarations
}

Answer 5

when we include some header files like iostream, we must unlock its doors to use them, like cout or cin and ... . so we use using namespace std; to unlock all of them.
we could use : std::cin; std::cout; to unlock only cin and cout instead of unlocking all.

Answer 6

it won't run until you declare them.
you can test these on a playground or an ide and see the results and errors.