CPSC120B
Fundamentals of Computer Science

Foldit

• Foldit
• Foldit Demo

Reading Questions

Quiz

Range

• We’ve already seen range with single input
• If we want different values for i, can write expressions to compute them
• For example if want to start at 1, add 1 to i
• There is an easier way, range has optional arguments
• If there are two arguments they are start and stop
• If there are three arguments they are start, stop, and step

Loop Patterns

• There are two different patterns to write the same program using loops

• For example a program that prints the positive even numbers less than 20 could be written using range to change the loop variable

  for i in range(2, 20, 2):
      print(i)

• Or, it could be written with an equation that uses the loop variable

  for i in range(1, 10, 1):
      print(i * 2)

• Using the range function pattern is often easier
• But using the loop variable equation pattern is more powerful
• It can be used to solve problems that the range function pattern can not

• For example, a series of numbers that does not increase the same amount every iteration of the loop such as the powers of two (2, 4, 8, 16, …)

  for i in range(1, 20, 1):
      print(2 ** i)

Loop Game

• The first activity for today is a game
• The game helps you practice these two patterns
• Complete the code to produce the desired graph
• Note, the ** operator does not exist, use *

New Lines

• Can specify that a print statement doesn’t end in a new line

  print("something", end=" ")
  print("something...")

• Whatever is inside of the quotes after end= will be used instead of a new line

• This is useful if you want to put everything a for loop prints on one line

  for i in range(3):
      print(i, end=" ")

• Note, this will leave a space at the end of the last print statement and no new line
• Can get a new line with print() after the loop

• How can you get rid of the extra space?

Range Peculiarities

• What happens if you use a floating point number?
• What happens if you use a floating point number that represents an integer?
• What happens if you flip the start and stop values?
• What happens if you start and stop at the same value?
• What happens if you change the loop varible, inside of the loop?

More Turtle

• goto tell the turtle to go to an x, y coordinate
• Where is the orgin?
• How big is the coordinate plane?
• setheading tell the turtle to turn to an orientation
• useful when turtle code is mixing forward and goto commands

Activity