Goals

• Link conditions with logical operators
• Understand and apply while-loops
• Program more complex decision structures

Linked Conditions

In some places, you get a heat day off under two conditions. The temperature must be over 30 degrees Celsius in the shade and it must be before 10:00 AM. You could also say: if temp >= 30 and shade == True and time < 10 must all be True.

Such links of conditions are connected to our language as clearly recognizable in the example above. If condition 1 is True AND condition 2 is True, then do something. Another way to link conditions is with logical OR.

Operator	Name	Example Condition	Value for x that gives True	Value for x that gives False
and	Logical AND	x > 0 and x < 10	5	0
or	Logical OR	x < 0 or x > 10	11	5
not	Logical NOT	not (x == 5)	3	5

import turtle
t = turtle.Turtle()

height = 160
age = 12

if height > 150 and age > 8:
    t.write("You may ride")
else:
    t.write("You may NOT ride")

Task

Change the program so that the person may ride.

import turtle
t = turtle.Turtle()

height = 
age = 
if height > 150 and age > 8:
    t.write("You may ride")
else:
    t.write("You may NOT ride")

While-Loops

We also know the while-loop from Karol.

repeat while IsWall
  TurnLeft
endrepeat

Here Karol repeats the TurnLeft until the condition is no longer met, meaning she's no longer in front of a wall.

Try to understand the Python program well before looking at the explanation:

import turtle
t = turtle.Turtle()

distance = 0
win = False
while win == False:
    t.left(12)
    t.forward(10)
    distance = distance + 10
    if distance > 100:
        win = True

:::detail Explanation Tobi is supposed to compete in a small race. He needs to cover distance and win. As long as he hasn't won, he must keep running (win == False). Now he runs 10 steps and it's checked whether he has already taken more than 100 steps. If so, he has won win = True and the condition win == False is no longer met. :::

Warning

Unlike many programming languages, the content of the loop in Python is indented by one tab. Never forget the colon at the end of the loop.

Tasks

Task 1: Entry Control

Write a program for a disco. A person can only enter if they:

• Are at least 18 years old AND have a ticket
• OR if they have VIP status (regardless of age)

Task 2: Countdown

Create a countdown from 10 to 0 with a while-loop. Tobi should write each number individually.

Task 3: Dice Game

Simulate rolling dice until a 6 comes up. Count how many times you rolled.

Tip

Use import random and random.randint(1,6) for the dice.

Preparation for Block 4

Think about when you would use a while-loop and when you would better use a loop with a fixed number of repetitions.