CPSC120B
Fundamentals of Computer Science

Bottle Bank

• Bottle Bank

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]')

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