Lecture Notes on 16 Sep 2009

Binary and Hexadecimal Numbers
0000  0
0001  1
0010  2
0011  3
0100  4
0101  5
0110  6
0111  7
1000  8
1001  9 
1010  A  10
1011  B  11
1100  C  12
1101  D  13
1110  E  14
1111  F  15

* 73 (10) = 1001001 (2) = 111 (8) = 49 (16)

* 7AD (16) = 0111 1010 1101 (2)
           = 1965 (10)

* Write a Boolean expression that evaluates to True if n is divisible
  by 3 and not by 7

  (n % 3 == 0) and (n % 7 != 0)

* Write a Boolean expression that evaluates to True if n is an odd two
  digit number

  (n >= 10) and (n <= 99) and (n % 2 != 0)

* Consider the following Boolean expression for what value of n is it
  True and for what value of n is it False?

  ((n % 100 != 0) and (n % 4 == 0)) or (n % 400 == 0)

  True: n = 2000
  False: n = 2009

# Write a program that prompts the user to enter the time in seconds
# and writes out the number of hours, minutes, and seconds

def main():
  # Prompt the user to enter time in seconds
  time = input ("Enter time in seconds: ")

  # Time less than 1 minute
  if (time < 60):
    print "Time is:", time, "second"

  # Time is between 1 minute and 1 hour
  if ((time >= 60) and (time < 3600)):
    min = time / 60
    sec = time % 60
    print "Time is:", min, "minute", sec, "second"

  # Time is greater than or equal to an hour
  if (time >= 3600):
    hour = time / 3600
    sec = time % 3600
    min = sec / 60
    sec = sec % 60
    print "Time is:", hour, "hour", min, "minute", sec, "second"

main()

# Prompt the user to enter positive numbers. The user ends input by
# typing a negative number. Write out the count of the numbers entered,
# their sum and average

def main():
  # Intialize count and sum
  count = 0
  sum = 0

  # Prompt the user to enter a number
  num = input ("Enter a number: ")

  # Prompt repeatedly for input
  while (num >= 0):
    count = count + 1
    sum = sum + num
    num = input ("Enter a number: ")

  # Write the count, sum, and average
  if (count == 0):
    print "Count = ", count
  else:
    avg = float (sum) / count
    print "Count = ", count, " Sum = ", sum, " Average = ", avg

main()

# Prompt the user to enter a number and then print the reverse of it
def main():
  # Prompt the user to enter a number
  num = input ("Enter a number: ")

  while (num < 0):
    num = input ("Enter a number: ")

  revNum = 0
  while (num > 0):
    revNum = (revNum * 10) + (num % 10)
    num = num / 10

  print "Reverse number: ", revNum

main()