Bsrgvty

I would like to improve the following code : my problem is explained in the screenshot.

documentclassarticle

usepackage[utf8]inputenc

usepackagetikz
usetikzlibraryshapes,arrows,calc


begindocument
pagestyleempty

% Source: http://www.texample.net/tikz/examples/simple-flow-chart/


% Define block styles
tikzstyledecision = [diamond, draw, fill=green!20, 
 text width=5.5em, text badly centered, node distance=2.5cm, inner sep=0pt]
tikzstyleblock = [rectangle, draw, fill=blue!20, 
 text width=5.5em, text centered, node distance=2.5cm, rounded corners, minimum height=2em]
tikzstyleloop = [rectangle, draw, fill=green!20, 
 text width=5.5em, text centered, node distance=2.5cm, rounded corners, minimum height=2em]
tikzstyleline = [draw, -latex']
tikzstylecloud = [draw, ellipse,fill=red!20, node distance=2.5cm,
 text width=6.5em, text centered, minimum height=2em]


begintikzpicture[node distance = 2cm, auto]
 % Place nodes
 node [cloud] (input) $(n ; x) in N times R$;
 node [block, below of=input] (affect1) $u leftarrow x$; 
 node [loop, below of=affect1] (whileinit) $i leftarrow 1$;
 node [decision, below of=whileinit] (whiletest) $i leq n$; 
 node [block, below of=whiletest] (affect2) $u leftarrow A_1(u)$;
 node [loop, left of=affect2] (whilenext) $i leftarrow i + 1$;
 node [cloud, below of=affect2] (output) $u$;

 path[line] (input) -- (affect1);
 path[line] (affect1) -- (whileinit);
 path[line] (whileinit) -- (whiletest);
 path[line] (whiletest) -- node oui (affect2);
 path[line] (affect2) -- (whilenext);
 path[line] (whilenext) |- (whiletest);
 path[line] (whiletest.east) -| node non ($(whiletest)!.7!(output.east)$) -| (output.north);% (output);
endtikzpicture

enddocument

Your problems can be solved by

1. loading and using the positioning library and


2. changing the non path.

The first point means that e.g. below of= needs to go to below=<distance> of. The distance can be omitted in which case the node distance values get used. As for the second point, I used

path[line] (whiletest.east) -- ++ (2cm,0) node[right] non |-
 ([yshift=-5mm]affect2.south) -- (output.north);

where 2cm controls the distance, and you may adjust this to your likings. In addition I replaced tikzstyle by the corresponding tikzset syntax.

documentclassarticle

usepackage[utf8]inputenc

usepackagetikz
usetikzlibraryshapes,arrows,calc,positioning


begindocument
pagestyleempty

% Source: http://www.texample.net/tikz/examples/simple-flow-chart/


% Define block styles
tikzsetdecision/.style=diamond, draw, fill=green!20, 
 text width=5.5em, text badly centered, node distance=2.5cm, inner sep=0pt,
block/.style=rectangle, draw, fill=blue!20, 
 text width=5.5em, text centered, node distance=2.5cm, rounded corners, minimum height=2em,
loop/.style=rectangle, draw, fill=green!20, 
 text width=5.5em, text centered, node distance=2.5cm, rounded corners, minimum height=2em,
line/.style=draw, -latex',
cloud/.style=draw, ellipse,fill=red!20, node distance=2.5cm,
 text width=6.5em, text centered, minimum height=2em


begintikzpicture[node distance = 1cm and 0.8cm, auto]
 % Place nodes
 node [cloud] (input) $(n ; x) in N times R$;
 node [block, below=of input] (affect1) $u leftarrow x$; 
 node [loop, below=of affect1] (whileinit) $i leftarrow 1$;
 node [decision, below=of whileinit] (whiletest) $i leq n$; 
 node [block, below=of whiletest] (affect2) $u leftarrow A_1(u)$;
 node [loop, left=of affect2] (whilenext) $i leftarrow i + 1$;
 node [cloud, below=of affect2] (output) $u$;

 path[line] (input) -- (affect1);
 path[line] (affect1) -- (whileinit);
 path[line] (whileinit) -- (whiletest);
 path[line] (whiletest) -- node oui (affect2);
 path[line] (affect2) -- (whilenext);
 path[line] (whilenext) |- (whiletest);
 path[line] (whiletest.east) -- ++ (2cm,0) node[right] non |-
 ([yshift=-5mm]affect2.south) -- (output.north);% (output);
endtikzpicture

enddocument

Here is a way:

documentclassarticle

usepackage[utf8]inputenc

usepackagetikz
usetikzlibraryshapes,arrows,calc


begindocument
pagestyleempty

% Source: http://www.texample.net/tikz/examples/simple-flow-chart/


% Define block styles
tikzstyledecision = [diamond, draw, fill=green!20, 
 text width=5.5em, text badly centered, node distance=2.5cm, inner sep=0pt]
tikzstyleblock = [rectangle, draw, fill=blue!20, 
 text width=5.5em, text centered, node distance=2.5cm, rounded corners, minimum height=2em]
tikzstyleloop = [rectangle, draw, fill=green!20, 
 text width=5.5em, text centered, node distance=2.5cm, rounded corners, minimum height=2em]
tikzstyleline = [draw, -latex']
tikzstylecloud = [draw, ellipse,fill=red!20, node distance=2.5cm,
 text width=6.5em, text centered, minimum height=2em]


begintikzpicture[node distance = 2cm, auto]
 % Place nodes
 node [cloud] (input) $(n ; x) in N times R$;
 node [block, below of=input] (affect1) $u leftarrow x$; 
 node [loop, below of=affect1] (whileinit) $i leftarrow 1$;
 node [decision, below of=whileinit] (whiletest) $i leq n$; 
 node [block, below of=whiletest] (affect2) $u leftarrow A_1(u)$;
 node [loop,left] at ($(affect2)+(-3,0)$) (whilenext) $i leftarrow i + 1$;
 node [cloud, below of=affect2] (output) $u$;

 path[line] (input) -- (affect1);
 path[line] (affect1) -- (whileinit);
 path[line] (whileinit) -- (whiletest);
 path[line] (whiletest) -- node oui (affect2);
 path[line] (affect2) -- (whilenext);
 path[line] (whilenext) |- (whiletest);
 path[line] (whiletest.east) -| node non ($(whiletest)!.7!($(output.east)+(3,0)$)$) -| (output.north);% (output);
endtikzpicture

enddocument

I just used your code and improved the requested things by just adding (-3,0) or (3,0) to your given positions. I think this is something easy to learn and can give you much more flexibility than creating the code from scratch -in my way- and instead of introducing just this simple thing to you.