Introduction to Programming

# Loops for Easy Squares

Here is how some students solve the last exercise, using variables to draw a square.

import turtle
tina = turtle.Turtle()
tina.shape("turtle")

forward = 50
left = 90

tina.forward(forward)
tina.left(left)

tina.forward(forward)
tina.left(left)

tina.forward(forward)
tina.left(left)

tina.forward(forward)
tina.left(left)

Notice that there is a lot of repetition in this program. Can we make this program shorter by getting rid of the repetition? Yes, we can, with loops. A loop is a bit of code that causes the computer to do something multiple times. Here is a loop for printing "Hello!" mutiple times. How many times do you think it will print?

Let's look at that in more detail:

for i in range(4):
    print("Hello!")

The first line in the loop defines the loop and tells us how many times to do the body of the loop. The body of the loop, the print("Hello!") part, is indented. The range part will run the number of times inside the parenthesis, in this case 4.

The i part is also special; it is a variable. So, you could print it out too.

for i in range(4):
    print("Hello!", i)

# Make a Better Square.

Here is our way of solving the square exercise. Can you edit this program to make it much better, by replacing the repetition with a loop?

Once you have used a loop to help Tony make a square, try making other shapes, like a triangle, a pentagon, or a hexagon, or maybe even a ... hendecagon. (if you can figure out what that is. )

# Badgers Badgers Badgers

Use for loops (you will need more than one) to print the following lyrics from the Badger Song. You can only use the words “Badger”, “Mushroom” and “Snake” once each in your code.

Print 2 verses of the song as follows:

Badger, Badger, Badger, Badger, Badger, Badger, Badger,Badger, 
Badger,Badger, Badger, Badger, Mushroom, Mushroom

Badger, Badger, Badger,Badger, Badger, Badger, Badger,Badger, 
Badger, Badger, Badger, Badger, Mushroom, Mushroom

A Snake!!!

Or maybe: 🦡🦡🦡🦡🦡🦡🦡🦡🦡🦡🦡🦡🍄🍄 🦡🦡🦡🦡🦡🦡🦡🦡🦡🦡🦡🦡🍄🍄 🐍

# More about range

Another interesting things with the loops is that range can have more than one number in it. If we put in two numbers, the values of i will go from the first number to one minus the second number, so if you want to print out the numbers 4, 5, 6, 7, you would use range(4,8):

for i in range(4, 7):
    print("Hello!", i)

Try that yourself. Write a program to print "Hello" next to all of the numbers from 10 to 20:

But there are more interesting things about range(): It can take a third number, and all three of the numbers can be negative or positive. So you could also type range(10,20, 2) or range(20,10,-1). Let's explore range () to figure out what the third number does.

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