Question

Currently in the process of learning C++, I picked up a free ebook titled "How to Think Like a Computer Scientist, C++ Edition." In the book, the "Hello world" program is given as:

#include // main: generate some simple output void main () { cout << "Hello, world." << endl; return 0 } The book was published during 1999, so I can assume that some things have changed. Now, I was under the impression that "void" does NOT return anything? Was it different in the past? Obviously, trying to run this code gives me an error, but I want to understand more about this.

Answer 1

Firstly, with a modern C++ compiler, you shouldn't use 'void' with main. Instead, use int; must be a terrible book if it uses void main() everywhere O.o:

int main()
{
// program
return 0;
}


nowadays, you would only need to write
#include <iostream>
instead of the old-style:
#include <iostream.h>

also, you need to prefix both cout and endl by std:: , so the program looks like
std::cout << "Hello, world." << std::endl;

or you can add the line
using namespace std;

so you don't have to prefix cout and endl by std::

A working program looks like

#include <iostream>
using namespace std;

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

Answer 2

why is it all different from the book?

About using int main() over void main():

every C++ program must pass a return code of type int back to the operating system, which is why main must always be declared int and should include a `return' statement somewhere in the main function. Actually, you can ignore having to include `return 0' since the compiler will automatically do it for you anyway, as long as you declare main as returning int (and not void).

about prefixing everything with std::, or having to use `using namespace std;'

C++ has something called namespaces, and if you wish to use anything that comes from the C++ standard library (things like cout and endl), you have to prefix them with std::, or have the line `using namespace std;' in order to let the compiler know that these objects are from the C++ standard library.

Answer 3

Wow... Well, so far the book uses void for main() in all the examples I've found. o.O Perhaps I should go with a more up-to-date book. At least I have the C++ pocket reference from O'Reilly to help, though.

Answer 4

Thanks for the clarification! :)

Answer 5

I learned some rudimentary C++ through Bucky Robert's video tutorials:
http://www.youtube.com/watch?v=tvC1WCdV1XU&list=PLC6E50B89DA30C77A&index=1&feature=plpp_video

For textbooks, I would check out some of the texts listed here:
http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list

Answer 6

Excellent! I will check those out, indeed. :D

Answer 7

I love Bucky. He was a great help when learning Java.