I would like to make a draw application. I want to enter user names until eg "end" is entered and then the program to split them in groups of two. Can you suggest any examples? I don't know how to start! If possible, I want to be Cross-platform. If it isn't possible I want linux.
Assuming I'm understanding your question correctly:
Pseudocode:
while the user is entering user names
store the user name in a list
for half the number of items in the list
remove a random item from the list
add that item to a second list
Here's a tutorial on using the STL container classes. You'll probably want to go with the std::list
: http://www.yolinux.com/TUTORIALS/LinuxTutorialC++STL.html
The iostream
libraries in C++ are for reading and writing lines of text through a command line interface:
http://en.wikipedia.org/wiki/Command_line_interface
On the plus side of these libraries, they are very standardized and every C++ compiler offers them. They work on Windows, Linux, or any other platform.
On the downside of these libraries, you can only read and write lines of text. You cannot draw circles around your names, or position them freely in the window. The only kind of "drawing" you can achieve with them is ASCII art.
This tutorial shows you basic input and output in C++:
http://www.cplusplus.com/doc/tutorial/basic_io/
If you want more freedom in drawing arbitrary graphics, that's not part of the C++ language specification. You'll need a third-party library, which may or may not be provided on multiple platforms.
Some of these libraries have routines for drawing text strings on the display in arbitrary fonts. Others just provide a display area and expect you to do text drawing yourself or with a library like FreeType:
http://stackoverflow.com/questions/52431/how-do-i-draw-text-using-opengl-sdl-and-c
It's probably best to avoid the complexity of graphics if you're just getting started with C++ as a language. Better to follow along with a few more basic tutorials, and you should be able to adapt the pseudocode Cogwheel gave you to get it. (People on StackOverflow don't like to directly write code for simple problems because that often amounts to doing someone else's homework.)