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‎en/_sources/conditional_loops.txt‎

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@@ -4,8 +4,68 @@ Conditional Loops
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Introduction
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============
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Conditional loops are way to repeat something until a certain condition is met.
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If the condition is never met, the loop can become infinite. In Python
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conditional loops are defined with the ``while`` statement::
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counter = 0
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while counter < 10:
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print "in the loop"
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counter += 1
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Move until condition is met
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===========================
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Exercise
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--------
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Use the ``while`` loop to move the turtle forward until it reaches the end of
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the window.
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Solution
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--------
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::
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def move_to_window_border(distance):
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while xcor() + distance < window_width() / 2:
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forward(distance)
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Bonus
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-----
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Can you make the turtle move exactly to the window border?
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Draw a spiral
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=============
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Loops can be interrupted with the ``break`` statement. This is often used in
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combination with infinite loops.
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Exercise
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========
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--------
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Write a ``while`` loop with a condition that is always true to draw a spiral.
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Interrupt the loop when the turtle reaches a certain distance from the center.
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Use the function ``distance(x, y)`` to get the turtle's distance to the point
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defined by the coordinates ``x`` and ``y``.
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.. note::
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To draw a spiral, the turtle has to rotate by a constant value and move
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forward by an increasing value in each repetition.
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Solution
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--------
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::
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def draw_spiral(radius):
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speed = 1
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while True:
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forward(speed)
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left(10)
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speed += 0.1
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if distance(0, 0) > radius:
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break
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‎en/_sources/conditionals.txt‎

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Conditional statements
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**********************
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Introduction
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============
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So far we have accomplished predefined tasks, but in all honesty we were accomplishing no better achievements than the 18th century automata, or the music boxes following one set of instruction to the end. What makes programming so much more powerful is conditional statements. This is the ability to *test* a variable (or a name) against a value and act in one way if the condition is met by the variable or an other way if not. They are also commonly called by programmers *if statements*.
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So far we have accomplished predefined tasks, but in all honesty we were accomplishing no better achievements than the 18th century automate, or the music boxes following one set of instruction to the end. What makes programming so much more powerful is conditional statements. This is the ability to *test* a variable (or a name) against a value and act in one way if the condition is met by the variable or an other way if not. They are also commonly called by programmers *if statements*.
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To know if a condition is *True* of *False*, we need a new type of data:
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the booleans. They allow logical operations.
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A logic statement or operation can be evaluated to be *true* or *false*.
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Our conditional statement can then be understood like this:
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**if** *(evaluation of a condition returns true)* **then** *do some operation* **else** *do an other operation*.
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And any operation that can be avaluated as *true* or *false* can but put to the test. All comparisons return *true* or *false*: *=,>,<*.
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And any operation that can be evaluated as *true* or *false* can but put to the test. All comparisons return *true* or *false*: *=,>,<*.
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Examples
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.. note::
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* We start from the center of the screen, which has coordinate (0;0)
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* We won't turn, until we reach the boundery our turtle wants to get away as quickly as possible
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* We won't turn, until we reach the boundary our turtle wants to get away as quickly as possible
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* We can get the x coordinate of our turtle with the function *xcor*
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* We can get the width of the screen with the function *window_width*
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‎en/_sources/functions_parameters.txt‎

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Introduction
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============
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Now we know how to *factorise* this code a little. But functions as we have defined them so far are not flexible. the variables are defined inside the function,
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and we need to rewrite a whole function to cahnge the value of an angle, or a distance in it.
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Now we know how to *factorize* this code a little. But functions as we have defined them so far are not flexible. The variables are defined inside the function, and we need to rewrite a whole function to change the value of an angle, or a distance in it.
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That is why we need to be able to give parameters, or also called *arguments* so that *names* we use in the function can be used with different values each time we call the function:
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backward(length)
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A parameterised function for a variable size hexagon
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A parameterized function for a variable size hexagon
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====================================================
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Exercise

‎en/_sources/index.txt‎

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loops
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functions_parameters
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conditionals
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logical_operators
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conditional_loops
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logical_operators

‎en/_sources/logical_operators.txt‎

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Logical operators
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=========================
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*****************
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We can also do some more complex things with
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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*)
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Introduction
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============
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Conditionals are a nice way to make decisions by asking if something equals true
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or not. But often one condition is not enough. For instance if we want to make a
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decision upon ``xcor()`` and ``ycor()`` we have to combine them. This can be
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done with logical operators.
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This and that or something else
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===============================
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Two easy to understand operators are ``and`` and ``or``. They do exactly whay the
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sound like: combine two statements in a way both have be true (``and``) or
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one of them has to be true (``or``)::
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if 1 < 2 and 4 > 2:
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print "condition met"
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if 1 < 2 and 4 < 10:
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print "condition not met"
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if 4 < 10 or 1 < 2:
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print "condition met"
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You are not restricted to one logical operator. You can combine as may as you
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want.
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Exercise
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--------
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Create a function that accepts the argument ``angel`` and moves the turtle into
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that direction until either the vertical or horizontal distance to the center
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exeeds 100.
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Solution
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--------
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::
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def move_to_square_border(angel):
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left(angel)
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while xcor() > -100 and xcor() < 100 and ycor() > -100 and ycor() < 100:
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forward(10)
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Bonus
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-----
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Execute the ``move_to_square_border()`` function multiple times with different
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angels. Use the ``home()`` function to make the turtle jump to the center after
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each line.

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