What's namespace and what's it's use and why main function is declared inside namespace........

Answer 1

A namespace is designed for providing a way to keep one set of names separate from another. The class names declared in one namespace does not conflict with the same class names declared in another.
for ex:- namespace definition or declaration

namespace namespace_name
{
// code declarations
}

complete program code:-

using System;
namespace first_space
{
class namespace_cl
{
public void func()
{
Console.WriteLine("Inside first_space");
}
}
}

namespace second_space
{
class namespace_cl
{
public void func()
{
Console.WriteLine("Inside second_space");
}
}
}

class TestClass
{
static void Main(string[] args)
{
first_space.namespace_cl fc = new first_space.namespace_cl();
second_space.namespace_cl sc = new second_space.namespace_cl();
fc.func();
sc.func();
Console.ReadKey();
}
}

explanation - here in this program both namespace has same name class but it does not effect the yield output.

Answer 2

output :-

Inside first_space
Inside second_space