15-110: Principles of Computing - Week 3

Conditionals and loops

• Blocks of code, importance of indentation

• Conditional statements

  • if statements

    
    def limit(n, upperBound):
        if (n > upperBound):
            n = upperBound
        return n
    

  • if ... else

    
    def evenOdd(word):
        n = len(word)
        if (n % 2 == 0):
            return "even"
        else:
            return "odd"
    

  • if ... elif ... else

    
    def letterGrade(points):
        if (points >= 90):
            letter = "A"
        elif (points >= 80):
            letter = "B"
        elif (points >= 70):
            letter = "C"
        elif (points >= 60):
            letter = "D"
        else:
            letter = "R"
        return letter
    

  • nested conditional statements

  
  def weatherAdvice():
      print "Please answer yes or no."
      answer1 = raw_input("Is it cold outside? ")
      if (answer1 == "yes"):
          print "You'd better wear a sweather."
          answer2 = raw_input("Is it raining? ")
          if (answer2 == "yes"):
              print "You'd better carry an umbrella."
          else:
              print "Good, at least it's not raining!"
      else:
          print "Enjoy the warm weather!"
  

• while loops

  
  def powersOfTwo(upperLimit):
      n = 1
      while (n < upperLimit):
          print n
          n *= 2
  

  
  def functionsRace(finishLine):
      print "Functions race!"
      print "Function 1: y1 = 10 * x + 50"
      print "Function 2: y2 = x * x - 100"
      print "x\ty1\ty2"
      x = 0
      y1 = 0
      y2 = 0
      # while loop with conjunct condition
      while (y1 < finishLine and y2 < finishLine):
          y1 = 10 * x + 50
          y2 = x * x - 100
          print "%d\t%d\t%d" % (x, y1, y2)
          x += 1
      if (y1 > y2):
          print "Function 1 wins!"
      elif (y1 < y2):
          print "Function 2 wins!"
      else:
          print "It's a tie!"
  

Readings from the book

Chapter 2 (pp. 29-36).

Suggested exercises from the book

Chapter 2: problems 1, 2, 6, 9, 17, 18, 19.