Added sections about logical operators and while loops

foonicorn · foonicorn · commit 3168811dc6f4 · 2012-08-30T01:07:34.000+02:00
diff --git a/docs/en/conditional_loops.rst b/docs/en/conditional_loops.rst
@@ -4,8 +4,68 @@ Conditional Loops
 Introduction
 ============
 
+Conditional loops are way to repeat something until a certain condition is met.
+If the condition is never met, the loop can become infinite. In Python
+conditional loops are defined with the ``while`` statement::
+
+    counter = 0
+    while counter < 10:
+        print "in the loop"
+        counter += 1
+
+Move until condition is met
+===========================
+
+Exercise
+--------
+
+Use the ``while`` loop to move the turtle forward until it reaches the end of
+the window. 
+
+Solution
+--------
+
+::
+
+    def move_to_window_border(distance):
+        while xcor() + distance < window_width() / 2:
+            forward(distance)
+
+Bonus
+-----
+
+Can you make the turtle move exactly to the window border?
+
+Draw a spiral
+=============
+
+Loops can be interrupted with the ``break`` statement. This is often used in
+combination with infinite loops.
 
 Exercise
-========
+--------
+
+Write a ``while`` loop with a condition that is always true to draw a spiral.
+Interrupt the loop when the turtle reaches a certain distance from the center.
+Use the function ``distance(x, y)`` to get the turtle's distance to the point
+defined by the coordinates ``x`` and ``y``.
+
+.. note::
+
+   To draw a spiral, the turtle has to rotate by a constant value and move
+   forward by an increasing value in each repetition.
+            
+Solution
+--------
+
+::
 
+    def draw_spiral(radius):
+        speed = 1
+        while True:
+            forward(speed)
+            left(10)
+            speed += 0.1
+            if distance(0, 0) > radius:
+                break
 
diff --git a/docs/en/index.rst b/docs/en/index.rst
@@ -14,5 +14,5 @@ Table of contents:
     loops
     functions_parameters
     conditionals
-    logical_operators
     conditional_loops
+    logical_operators
diff --git a/docs/en/logical_operators.rst b/docs/en/logical_operators.rst
@@ -1,7 +1,53 @@
 Logical operators
-=========================
+*****************
 
-We can also do some more complex things with 
-We can return the opposite of a logic operation, with **not** as a keyword in front of your expression, or combine several logic statements together with logical **and** and **or** links between them (they are usually called *operators*)
+Introduction
+============
 
+Conditionals are a nice way to make decisions by asking if something equals true
+or not. But often one condition is not enough. For instance if we want to make a
+decision upon ``xcor()`` and ``ycor()`` we have to combine them. This can be
+done with logical operators.
 
+This and that or something else
+===============================
+
+Two easy to understand operators are ``and`` and ``or``. They do exactly whay the
+sound like: combine two statements in a way both have be true (``and``) or
+one of them has to be true (``or``)::
+
+    if 1 < 2 and 4 > 2:
+        print "condition met"
+
+    if 1 < 2 and 4 < 10:
+        print "condition not met"
+
+    if 4 < 10 or 1 < 2:
+        print "condition met"
+
+You are not restricted to one logical operator. You can combine as may as you
+want.
+
+Exercise
+--------
+
+Create a function that accepts the argument ``angel`` and moves the turtle into
+that direction until either the vertical or horizontal distance to the center
+exeeds 100.
+
+Solution
+--------
+
+::
+
+    def move_to_square_border(angel):
+        left(angel)
+        while xcor() > -100 and xcor() < 100 and ycor() > -100 and ycor() < 100:
+            forward(10)
+
+Bonus
+-----
+
+Execute the ``move_to_square_border()`` function multiple times with different
+angels. Use the ``home()`` function to make the turtle jump to the center after
+each line.
