CPSC120B
Fundamentals of Computer Science

Reading Questions

Quiz

Practice Session

• Sunday - 6PM - Trexler 363 (i.e. our classroom)

Accumulating

• The accumulator pattern is updating variables inside of a loop

• Recall the square spiral program

  delta_dist = 10
  dist = delta_dist
  turtle.forward(dist)
  turtle.left(90)
  dist = dist + delta_dist
  turtle.forward(dist)
  turtle.left(90)
  dist = dist + delta_dist
  turtle.forward(dist)
  turtle.left(90)
  dist = dist + delta_dist
  turtle.forward(dist)
  turtle.left(90)
  dist = dist + delta_dist

• That’s a lot of copying and pasting that would be better in a loop

  delta_dist = 10
  dist = delta_dist
  for i in range(10):
      turtle.forward(dist)
      turtle.left(90)
      dist = dist + delta_dist

• It is also possible to do it without the accumulator

  for i in range(10):
      turtle.forward(i * 10 + 10)
      turtle.left(90)

• It could even be done using range

  for i in range(10, 100, 10):
      turtle.forward(i)
      turtle.left(90)

• Note, however, that not all problems can be solved with range
• Range does not work for multiple values or values which change non-linearly
• Also note, not all problems can be solved with equations using the loop variable

• Loop variable equations do not work if the value is not predicable (i.e. user input or randomization)

Lab