# knerr cs21 notes...

back to schedule
```
WEEK03: booleans, logical operators, conditionals (if/else)
---------------------------------------------------------------
W: review expressions, if/else, logical operators

EXPRESSIONS:

>>> x = 10
>>> y = 20
>>> x > y
False
>>> x < y
True
>>> x == y
False

can also do this with letters

>>> ch = 'a'
>>> ch =='b'
False
>>> ch != 'b'
True
>>> ch > 'b'
False
>>> ch < 'b'
True

CONDITIONAL STATEMENTS:

if < condition > :
do this
and this
else:
do that

--> can do if without an else

>>> if i < j:
...   print "i is less than j"
...
i is less than j

>>> if i == j:
...   print "i and j are equal"
... else:
...   print "i is not equal to j"
...
i is not equal to j
>>>

answer = raw_input("would you like to play a game? (y/n): ")

print ">>> SUPER. let's play tic-tac-toe..."
else:
print "ok...quitting"

LOGICAL OPERATORS: and or not (in ??)

--> can combine conditions with "and" and "or"

>>> if speed < 70 and speed > 40:
...    print "no ticket...you can go"
... else:
...    print "you're either going too fast or two slow!"

--> can you impove the above play-a-game program to handle
more cases?

\$ python playgame.py
would you like to play a game? (y/n): yes
>>> SUPER. let's play tic-tac-toe...

\$ python playgame.py
would you like to play a game? (y/n): Yes
>>> SUPER. let's play tic-tac-toe...

--> can you write this program:

\$ python lettercase.py
phrase: Hello!
uppercase:  H
lowercase:  e
lowercase:  l
lowercase:  l
lowercase:  o
nonletter:  !

HINT:

>>> ch = 'g'
>>> ch > 'a' and ch < 'z'
True
>>> ch = 'G'
>>> ch > 'a' and ch < 'z'
False
>>>

--> can you write this program:

\$ python isodd.py