Concept: Schleifen

Die for-Schleife

Die for-Schleife wiederholt -vereinfacht gesprochen- einen Befehl n-mal:

Example

The following loop will run 5 times:

for i in range(5):
    print("I'm in a loop!")

The program produces the following output

I'm in a loop!
I'm in a loop!
I'm in a loop!
I'm in a loop!
I'm in a loop!

The counter variable

You can use the variable i as a counter variable. It counts up (starting from 0):

Example

for i in range(5):
    print(i)

The program produces the following output

0
1
2
3
4

General form:

In der Regel schreibt man:

for i in range(max):
    <codeblock>

oder

for i in range(min, max):
    <codeblock>

You can specify how often the loop is run or specify certain ranges:

Beispiele: Mit Schleifen zeichnen

With loops, you can draw:

import miniworlds 

world = miniworlds.World(200, 200)

for i in range(4):
    miniworlds.Circle((20 + 50 * i, 50), 20)
    
world.run()

Schachbrettmuster

With the modulo operator, you can check if a result is divisible by 2, namely ``x divisible by 2 if and only if x % 2 == 0`

This can be used to draw checkerboard patterns by combining loops with an if statement:

from miniworlds import *

world = World(200, 50)

for i in range(4):
    rect = Rectangle((50 * i, 0), 50, 50)
    if i % 2 == 0:
        rect.color = (255,0,0, 255)
    else:
        rect.color = (255, 255, 255, 255)
    
world.run()

Graphen

Auch Graphen lassen sich auf diese Art zeichnen:

from miniworlds import *

world = World(400, 400)


for x in range(400):
    gl = 0.5*x + 50
    y = 400 - gl
    Point((x, y))
    
world.run()

Nested loops

With the help of nested loops, you can draw multidimensional patterns.

from miniworlds import *

world = World(200, 200)

for i in range(4):
    for j in range(4):
        Circle((20 + 50 * i, 20 + 50 * j), 20)
    
world.run()

Die while-Schleife

Die while-Schleife hat allgemein folgenden Aufbau:

while <Bedingung>:
    <code-block>

• As long as the condition is true, the loop will repeat over and over again. This also makes it possible to create infinite loops.

Example:

The following program generates a random pattern:

from miniworlds import *
import random
world = World(255, 60)
x = 0

while x < 255:
    c = Circle((x, 30), 20)
    c.color = (x,0,0,random.randint(0,255))
    x = x + random.randint(10,50)
    
world.run()

Die Hauptschleife

Your entire program technically runs within a while loop:

while <no quit>
  <draw images on screen>
  <handle logic and events>

The for loop is not suitable for this, as you need to know in advance how many iterations should be executed.

Loops innerhalb von registrierten Methoden

If you want to run a loop within the act method or an event method, then you need to know the following:

The entire loop within such a method is executed within a single frame. Therefore, a loop is not suitable here for moving a character, for example, since it is redrawn every frame - However, a loop runs completely within a frame.

Example

This can be well illustrated using the example of a traffic light system. The sequence of the loop can be well visualized with a state diagram.

        stateDiagram
    [*] --> Green

    Green --> GreenYellow
    GreenYellow --> Red
    Red --> RedYellow
    RedYellow --> Green
    

In code, you can implement this as follows:

from miniworlds import *

state = "green"

while True:
    if state == "green":
        state = "green-yellow"
        print("green")
    elif state == "green-yellow":
        state = "red"
        print("green-yellow")
    elif state == "red":
        state = "red-yellow"
        print("red")
    elif state == "red-yellow":
        state = "green"
        print("red-yellow")
world.run()

In the main loop, the while loop is “replaced” by the main loop:

from miniworlds import *

world = World(100,240)
state = "green"
g = Circle ((50,40), 40)
y = Circle ((50,120), 40)
r = Circle ((50,200), 40)

@world.register
def act(self):
    global state
    if world.frame % 20 == 0:
        if state == "green":
            g.color = (0,255,0)
            y.color = (255,255,255)
            r.color = (255,255,255)
            state = "green-yellow"
            print("green")
        elif state == "green-yellow":
            g.color = (0,255,0)
            y.color = (255,255,0)
            r.color = (255,255,255)
            state = "red"
            print("green-yellow")
        elif state == "red":
            g.color = (255,255,255)
            y.color = (255,255,255)
            r.color = (255,0,0)
            state = "red-yellow"
            print("red")
        elif state == "red-yellow":
            g.color = (255,255,255)
            y.color = (255,255,0)
            r.color = (255,0,0)
            state = "green"
            print("red-yellow")
world.run()

As you can see, the program code has only been changed in certain places, the program flow remains the same. The while loop is replaced here by the act method.