CPSC120B
Fundamentals of Computer Science

Reading Questions

Quiz

Logical Operators

• Numerical operators have numeric values for operands

• Logical operators (or Booean operators) have boolean values for operands

  print(True and False)
  print(False or True)
  print(not False)

• These are useful in conditional statements when you have complex conditions

• For example, if you want to check if a number is in a range

  x = int(input('enter an integer: '))
  if x >= 0:
      if x <= 100:
          print('you entered a number in the range [0, 100]')
      else:
          print('you did not enter an number in the range [0, 100]')
  else:
      print('you did not enter an number in the range [0, 100]')

• This can be simplified with a logical operator

  x = int(input('enter an integer: '))
  if x >= 0 and x <= 100:
      print('you entered a number in the range [0, 100]')
  else:
      print('you did not enter a number in the range [0, 100]')

• Note, the operands must be Booleans!

• The following will not work

  print(x == 1 or 2 or 3)
  print(x > 0 and < 10)

• Also note, and, or and not, do not have the same precedence

  x = 2
  print(not x == 1 or x == 2)

• Is not equivalent to

  x = 2
  print(not (x == 1 or x == 2))

Boolean Functions

• Can have variables equal to boolean values

  x = int(input('enter an integer: '))
  if x >= 0 and x <= 100:
      x_is_in_range = True
  else:
      x_is_in_range = False
  if x_is_in_range == True:
      print('you entered a number in the range [0, 100]')
  else:
      print('you did not enter a number in the range [0, 100]')

• Setting a variable to a Boolean value can usually be simplified by using an expression

  x = int(input('enter an integer: '))
  x_is_in_range = x >= 0 and x <= 100
  if x_is_in_range == True:
      print('you entered a number in the range [0, 100]')
  else:
      print('you did not enter a number in the range [0, 100]')

• This can make the code more readable
• Note that if x_is_in_range == True: is a little redundant

• It can be simplified to if x_is_in_range: which also reads a little better

  x = int(input('enter an integer: '))
  x_is_in_range = x >= 0 and x <= 100
  if x_is_in_range:
      print('you entered a number in the range [0, 100]')
  else:
      print('you did not enter a number in the range [0, 100]')

• Can also do this with a function that returns a Boolean value

  def is_in_range(x):
      return x >= 0 and x <= 100
  x = int(input('enter an integer: '))
  if is_in_range(x)
      print('you entered a number in the range [0, 100]')
  else:
      print('you did not enter a number in the range [0, 100]')

Example - Point in Circles

import graphics

POINT_WIDTH = 10

# PRE:  point_x, point_y, circle_x, circle_y, and circle_radius are
#       positive numbers
# POST: returns whether the specified point is inside the specified
#       circle
def is_point_in_circle(point_x, point_y, circle_x, circle_y, circle_radius):
    delta_x = circle_x - point_x
    delta_y = circle_y - point_y
    distance = (delta_x * delta_x + delta_y * delta_y) ** (1 / 2)
    return distance <= circle_radius

circle_offset = 50
circle_1_x = graphics.window_width() / 2 - circle_offset
circle_1_y = graphics.window_height() / 2
circle_1_radius = 100
circle_1_width = circle_1_radius * 2
circle_1_height = circle_1_width
circle_2_x = graphics.window_width() / 2 + circle_offset
circle_2_y = graphics.window_height() / 2
circle_2_radius = 100
circle_2_width = circle_2_radius * 2
circle_2_height = circle_2_width

graphics.clear()
graphics.draw_oval(circle_1_x, circle_1_y, circle_1_width, circle_1_height)
graphics.draw_oval(circle_2_x, circle_2_y, circle_2_width, circle_2_height)
while graphics.window_open():
    if graphics.button_down(1):
        point_x = graphics.mouse_x()
        point_y = graphics.mouse_y()
        in_circle_1 = is_point_in_circle(point_x, point_y,
                                         circle_1_x, circle_1_y,
                                         circle_1_radius)
        in_circle_2 = is_point_in_circle(point_x, point_y,
                                         circle_2_x, circle_2_y,
                                         circle_2_radius)
        if in_circle_1 or in_circle_2:
            graphics.draw_oval(point_x, point_y, POINT_WIDTH, POINT_WIDTH,
                               fill="green")
        else:
            graphics.draw_oval(point_x, point_y, POINT_WIDTH, POINT_WIDTH,
                               fill="red")
    graphics.wait()

Lab