/**

\page getting_started Getting Started

At the beginning we strongly suggest that you open your favorite text

editor and enter the code simultaneously as you read it. Compiling the

demos is also a good exercise.

As the first example we show you a lemon style "Hello World"

program. Now we explain almost every line, but later we will skip the

basics and focus on new things.

\section hello_world Hello World in LEMON

In this little program we give you a taste of the LEMON programming.

Let's see the code fragment to fragment!

\dontinclude hello_world.cc

\skip include

\until iostream

We want to use a \c lemon::ListGraph so the include goes like this:

\skip include

\until list_graph

The next few lines are not necessary but useful shortcuts, if you don't

want to type \c lemon::ListGraph::Node every time.

\skip using

\until Edge

For this demo we need to declare a ListGraph and a special NodeMap to

store the characters associated to the graph's nodes.  

\skip main

\until char_map

Adding nodes to the graph is very easy.

\skip new_node

\until addNode

When a new node or edge is added to the graph the assigned maps are automatically resized.

So graphs can be built dynamically. The usage of a map is very natural.

\skip char_map

\until char_map

Notice that no reference or additional assignment is needed to work with nodes.

They won't become illegal or won't lead to throwing any exceptions.

You can declare and handle a node like every other basic type such as \c int.

\skip Store

\until char_map

As one expects adding an Edge is similar. You need to define the \b source node

and the \b destination node. The nodes must belong to the graph of course. The

Edge has the direction from the source to the destination. In some cases you don't

want the edges to be directed - then you use an undirected graph. For example

lemon::ListUGraph.

\skip addEdge

\until addEdge

In the next few lines we add some more nodes and edges and to the graph we need.

Those lines are not very interesting so we skip them, but you find the whole

working program in file hello_lemon.cc in the demo section.

The next statement must be familiar. But what is that INVALID in the \c while

test statement? In LEMON we usually use the INVALID to check if an object

contains valid information.

\skip current_node

\until {

We take the current node and write out the character assigned to it. Is's easy

with the \c char_map.

\skip std

\until std

And here comes the trick. OutEdgeIt iterates on outgoing edges of a given node.

We pass the current node as argument to it, so the \c edge iterator will stand

on the first outgoing edge of the current node, or will be INVALID if the node

has no outgoing edges.

\skip edge

\until edge

The graph we built before is linear, so we know that it ends, when no more outgoing

edges found. Otherwise the current node must be the node the edge points to.

Basic information about an edge can be requested from the graph.

\skip if

\until }

Finish the code, just to be precise.

\skip return

\until }

\section compile_hw Compiling Hello World

To compile this program all you have to do is type in

\code g++ -ohw hello_world.cc \endcode

and press \c Enter! This is the case if you installed LEMON on your system.

(For more information see the LEMON installation instructions.)

This is because LEMON is template library and most of it's code has to be available

as source code during compilation.

Most programs using LEMON will compile as easy as this one unless you want to

use some performance measuring tools LEMON can provide. Then you need to link

an additional library against your program.

*/