CPSC120B
Fundamentals of Computer Science

The Cost of Poor Test Coverage

• 0.3 - 0.2 == 0.1
• U.S. Details Flaw in Patriot Missle

Reading Questions

Quiz

Booleans

• The Boolean type has only 2 values, True and False

• Boolean expressions evaluate to Boolean values

  print(1 == 2)
  print(1 != 2)
  print(1 < 2)
  print(1 > 2)
  print(1 <= 2)
  print(1 >= 2)

Conditionals

• Write code that executes only if a condition is met

• Boolean values are useful for specifying the conditions

  integer = int(input('enter an integer: '))
  if integer == 0:
      print('You entered Zero')
  else:
      print('You did not enter Zero')

• Can also leave off the else

• This can be toublesome if a variable is created in the if block

  x = 0
  if x != 0:
      y = x
  print(y)

• It is possible to put conditionals inside of conditionals

  number = int(input('enter an integer: '))
  if number < 10:
      if number > 0:
          print('you entered a number between 1 and 9')

• The print statement in the inner if statement is only executed if both the outer and the inner are true
• If either are false it is not executed
• If statements can also be inside of loops and loops can be inside of if statements
• Unsuprisingly they can also be inside of functions

• Note, returns and if statments can produce unexpected results

  def if_something(number):
      if number < 0:
          return number * -1
      print('you entered non-negative number')

• The above function only have a return statement inside of the if
• So if a positive number is given as input, it will return None
• And it will not print if a negative number is entered

• A good way to prevent these problems is to have just a single return statement as the final line of the function

Activity