This code cant keep cmd open.

I'm reading Accelerated C++ and on their first example they have the code:

Code:

---

// a small C++ program
#include <iostream>

int main()
{
    std::cout << "Hello, world!" << std::endl;
    return 0;
}

---

When it starts the cmd closes and won't display Hello, World!

However from another book I was taught to do it like this:

Code:

---

// a small C++ program
#include <iostream>

useing namespace std; // (I use this)

int main()
{
    cout << "Hello, world!\n";  // Instead of std::cout << just cout and I use \n for next line.
    return 0;
}

---

This code works fine, why is std::cout taught then?

std::cout allows you to call cout without switching namespaces. You can do it whichever way you want. This shouldn't have any affect on weather or not the command window closes.

So your saying instead of using "using namespace std;" (Might be useing don't no) you can just use std::cout instead?

EDIT: Ok I got it to work, I added this line before return 0;

Code:

---

std::cin.get();

---

So it works now! :D

Namespaces are there to avoid naming clashes. A lot of the time, it won't be a problem to put "using namespace std;" but if you use another library, you might have two classes/functions/variables/etc with the same name. For example:

Code:

---

#include <iostream>
int cin;

using namespace std;

int main()
{
  cin>>cin;
}

---

This will obviously generate an ambiguity error. It's easy to resolve, though:

Code:

---

#include <iostream>
int cin;

using namespace std;

int main()
{
  std::cin>>::cin;
}

---

Edit: Board's running really slow...Anyways, I was trying to say that a good reason to avoid "using" statements is for code like this:

Code:

---

#include <iostream>


using namespace std;

int main()
{
  int cin;
  cin>>cin;
}

---

Doesn't generate any compile errors but could easily lead to some problems

Thanks! I learned even in Visual Basic that you should use diffrent names for strings. On one of my books it has a big list of names to avoid using aswell! :) I must say learning C++ has been a lot of fun with the book I'm reading! Even though I'm an expert in VB, when I learn C++ I most likely will never use VB again. :)

I'm in the middle of Accelerated C++, and the authors, I believe, are just trying to have you learn and appreciate the concept of namespaces and the using statements over time. You start out with

Code:

---

std::cout

---

which specifies the cout within the std namespace for just this one use, then later you'll see instead

Code:

---

using std::cout;

---

near the beginning of your code, which lets the compiler know that you want to use the cout from the std namespace by default. (You can specify a different cout with something like other_namespace::cout within the program if you need to.) Eventually, I imagine, we'll get on to

Code:

---

using namespace std;

---

which says that you'll be exclusively using names from the std namespace, except where you opt out as above.

Alright thanks! I'm only on Chapter 2, about strings. Which I knew before but going through it all anyways. :)